Can a relationship exist that is mutualistic/parasitic/etc. but not considered symbiotic?

Can a relationship exist that is mutualistic/parasitic/etc. but not considered symbiotic?

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Wikipedia definition of symbiosis: "Symbiosis (from Greek σύν "together" and βίωσις "living")[2] is close and often long-term interaction between two or more different biological species."

Wikipedia definition of mutualism: "Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits from the activity of the other."

In intro biology class, I (and many other people, I'm sure) was taught that mutualism is a type of symbiosis. However, now that I think more about it, it seems like some relationships that are mutualistic don't appear to fit the definition of symbiotic. Some relationships are clearly mutualistic and symbiotic (humans and gut flora, for example) but other relationships (like bees pollinating flowers) are mutualistic but don't appear to fit the definition of "close and often long-term interaction". The same of course goes for parasitic, ammensalistic, etc. relationships as well.

Thoughts, anyone?

TL;DR: mutualistic/parasitic relationships are members of symbiotic relationships class

So, first of all, there is a way to look it up.

Secondly, the very same article in wiki has subsection on parasitism. Reading it would be useful:

This is also known as antagonistic or antipathetic symbiosis.

Also, brief search through Google Scholar will show how these words are used in context. papers include such as:

  1. Fungal symbiosis from mutualism to parasitism: who controls the outcome, host or invader?
  2. Mutualism and parasitism: the yin and yang of plant symbioses
  3. Mutualism or parasitism? The variable outcome of cleaning symbioses
  4. Enhanced growth as a manifestation of parasitism and shell deposition in parasitized mollusks. Aspects of the biology of symbiosis.

Chapter 2 Definitions of Types of Symbioses

This chapter presents the definitions of terms that describe heterospecific associations among organisms. Symbiosis means living together thus symbiosis is the broad, all-encompassing term used to describe all types of heterospecific associations, excluding predation, during which there exists physical contact or intimate proximity between the two members. There are no implications of benefit acquirement or giving, nutritional dependency, or infliction or receipt of harm. Thus symbiosis is a broad ecological term under which can be categorized parasitism, commensalism, mutualism, and phoresis. Parasitism describes a heterospecific relationship, permanent or temporary, during which there exists metabolic dependence of the parasite, the smaller of the two species, on its host. Commensalism describes intimate relationship during which the commensal generally derives physical shelter from the host, nourishes on foods that are associated but not a part of the host, and is not metabolically dependent on the host. A “predatory relationship” is defined as one during which one member, the predator, as a rule, rapidly kills and devours the other, the prey.

Commensalism Definition

The term was coined in 1876 by Belgian paleontologist and zoologist Pierre-Joseph van Beneden, along with the term mutualism. Beneden initially applied the word to describe the activity of carcass-eating animals that followed predators to eat their waste food. The word commensalism comes from the Latin word commensalis, which means "sharing a table." Commensalism is most often discussed in the fields of ecology and biology, although the term extends to other sciences.

Commensalism: A Positive/Zero Interaction

An interaction where one species benefits and the other remains unaffected is known as commensalism. As an example, cattle egrets and brown-headed cowbirds forage in close association with cattle and horses, feeding on insects flushed by the movement of the livestock. The birds benefit from this relationship, but the livestock generally do not. Often it's difficult to tease apart commensalism and mutualism. For example, if the egret or cowbird feeds on ticks or other pests off of the animal's back, the relationship is more aptly described as mutualistic.

3. Emerging symbiosis properties

Figure 4. Legume nodules. A, Nodosities due to Sinorhizobium meliloti bacteria on a Medicago root (note the pink color, due to an oxygen-carrying protein, leghemoglobin, Lb) B, View of a section of a nodosity due to Sinorhizobium meliloti bacteria on a Medicago root C, Transmission electron microscopy showing symbiotic bacteroids (b) (Bradyrhyzobium japonicum) in soybean root nodules, surrounded by an endocytosis membrane (white arrow) D, Nodosities metabolism, bacteroids ensure nitrogen fixation through a controlled supply of oxygen and carbonaceous substrates from the plant. A & B: [Source: © Ninjatacoshell (CC BY-SA 3.0) via Wikimedia Commons]. C: [Source: © Louisa Howard – Dartmouth Electron Microscope Facility, via Wikimedia Commons]. Further to the addition of partners’ capacities, mutualistic symbiosis expresses certain properties that separate partners do not have. First, at the morphological level, symbiosis creates structures that do not exist outside the association: this is the case of nodules (Figure 4A and B), organs induced by bacterial colonization whose anatomy differs from the roots (frequent absence of terminal meristem, vessels conducting peripheral sap, etc.). The structure of bacteria is also modified by living in the cell: loss of flagella, wall and increased size (as in nodules, Figure 4C). This modified morphology is called “bacteroids” due to small proteins injected into the bacteria by the plant.

Other emergences are functional. In the example of nodules (Figure 4D), the bacteroid uses energy obtained from its respiration to reduce -thanks to the nitrogenase Enzyme complex specific to certain prokaryotes that catalyzes the complete sequence of reactions during which the reduction of dinitrogen N2 leads to the formation of ammonia NH3. This reaction is accompanied by hydrogenation. – the atmospheric nitrogen N2 to ammonium NH3, which serves as a source of nitrogen for the plant (and bacteroid). Conversely, the plant provides carbon and oxygen supply. Oxygen is required for respiration, but nitrogenase is inactivated by oxygen: this contradiction explains why a free rhizobium Aerobic soil bacterium that can create symbiosis with legumes. These bacteria are found in nodules where they will fix and reduce atmospheric nitrogen, which can then be assimilated by the plant. In exchange plants provide carbonaceous substrates to bacteria. in the soil is unable to fix nitrogen. On the other hand, in the nodosity, oxygen does not diffuse freely, but is captured by a protein of the host cell, leghaemoglobin [7]. Located around the bacteroid, leghaemoglobin protects the nitrogenase from the inactivating effects of the oxygen and provides an oxygen reserve for bacteria respiration. Nitrogen fixation can therefore only be achieved within in the nodosity.

Many other functional traits are induced by symbiosis, such as some protective effects that rely on the induction of partner defences, tolerated by the symbiont but harmful to pathogens. Mycorrhizal fungi, for example, induce the accumulation of protective tannins at the root level, which are responsible for inducing an increased level of defence and reactivity throughout the plant, including the aerial parts. Thus, the mycorrhized plant reacts faster and more strongly to an herbivore or parasite than a non-mycorrhized control plant. In lichens, algae induce the fungus to synthesize secondary metabolites that have a protective role against strong light and herbivores.

Figure 5. Representation of the diversity of the human microbiome. In the centre is the phylogenetic tree representing the species of the microbiota. On the periphery, representation of specific microbiota (gut, stomach, mouth, vagina, etc.). [Source: Scheme reproduced from Morgan et al (2013) See ref. [9].] Overall, the phenotype All the observable characteristics of an individual. of the organism therefore also results from its symbionts, either by adding their capacities or because they modify it. The phenotype is therefore more than what the genome encodes. Symbionts and their genes are part of what Dawkins [8] calls an “extended phenotype”, that is, the set of elements recruited into the environment that modify the phenotype of a species. In humans, for example, the digestive tract contains a large number of bacterial species (Figure 5): metagenomic analysis applied to our intestine has shown that it contains nearly 100,000 billion microorganisms, ten times more than our own cells! This is called the microbiota (see Human microbiotas: allies for our health).

The gut microbiota All microorganisms (bacteria, yeasts, fungi, viruses) living in a specific environment (called microbiome) in a host (animal or plant). An important example is the set of microorganisms living in the intestine or intestinal microbiota, formerly called “intestinal flora”. is essential for the proper functioning of its human host, not only in terms of digestion or vitamin production, of course, but also for metabolism, immunity… or the nervous system. The imbalances in the intestinal flora are now suspected of being at the origin of a series of pathologies: obesity, diabetes, cardiovascular diseases, allergies, inflammatory diseases, even autism [2],[7]. The human microbiota is not limited to the digestive tract: international metagenomic programs have identified genes from a large number of symbiotic microorganisms living in the mouth, nose, vagina or on the skin (Figure 5).

Figure 6. Microbial modulation of interactions between a host and its parasites/pathogens. The action of the host genotype (represented by the blue ellipse) and all environmental factors that affect the composition of the microbiota will affect the interaction between the host and its parasites/pathogens, particularly through the immune system. [Source: Adapted from Gross et al. [See ref. 10]] The microbiota is able to modulate the interactions between a host and its parasites/pathogens (Figure 6). The action of the microbiota can be direct (competition) or indirect through its action on the establishment, maturation and functioning of the immune system. We know, by studying mice raised in an axenic Caracterise a culture (of prokaryotic or eukaryotic cells, tissues, living organisms) free of all saprophytic or pathogenic germs. environment, that the development of the nervous system and even the behaviour are partly influenced by it!

It has therefore been proposed that the unit relevant for biology or evolution should be less the organism than the symbiotic procession: we speak of holobionte means the biological unit composed of the host (plant or animal) and all its microorganisms. to name this entity more relevant to the importance of biotic interactions [11].


Mutualism is a relationship in which both species benefit. Mutualistic interaction patterns occur in three forms. Obligate mutualism is when one species cannot survive apart from the other. Diffusive mutualism is when one organism can live with more than one partner. Facultative mutualism is when one species can survive on its own under certain conditions. On top of these, mutualistic relationships have three general purposes. Trophic mutualism is exemplified in lichens, which consist of fungi and either algae or cyanobacteria. The fungi's partners provide sugar from photosynthesis and the fungi provide nutrients from digesting rock. Defensive mutualism is when one organism provides protection from predators while the other provides food or shelter: an example is ants and aphids. Dispersive mutualism is when one species receives food in return for transporting the pollen of the other organism, which occurs between bees and flowers.

List of 20 examples of mutualism

1- The bees and the flowers

The bees fly from flower to flower in search of nectar, which they transform into food, which benefits these insects.

On the other hand, whenever the bees are placed on a flower, particles of pollen adhere to their body Such particles are transported to other flowers, resulting in plant pollination.

It is observed, then, that this is a relationship of mutualism in which the bee obtains food and the plant reproduces itself.

2- Birds and flowers

Like bees, some birds feed on the nectar of flowers, transporting pollen from one plant to another, which favors pollination .

3- Bacteria and humans

Humans are not able to digest all the food we eat.

However, in our intestine, there is a certain type of bacteria (which forms the intestinal microbiota) that feeds on everything that the human body is not able to process and digests it partially, facilitating the work of the intestine.

4- Picabueyes and rhinos

Picabueyes are birds that perch on rhinoceroses and eat ticks and other parasites that live on the skin of these mammals.

In this relationship, both benefit since the birds get food while the rhinos have a pest control service.

Similarly, when it is possible that the rhinoceros is in danger, the picabuey alerts the other animals with their singing.

5 - Protozoa and termites

As with bacteria and humans, protozoa help termites digest food.

6- Anemones and Clown Fish

The tentacles of the anemones have stinging stings on the fish However, the mucus in the skin of the clown fish protects them from this sting.

Thanks to this, clown fish can live comfortably on anemones, protecting them from predators, such as butterflyfish.

7- The crab spider and the algae

Spider crabs spend much of their lives in areas where the water is shallow, which increases the possibility of being seen by predators.

However, on the back of these crabs, there is a certain type of algae that acts as a camouflage for the animal. In return, the plant gets a place to live.

8- Plants and humans

It is well known that plants and humans can not live without each other. This relationship of mutualism is based on the fact that humans breathe the oxygen produced by plants and expel carbon dioxide.

For their part, plants take carbon dioxide and use them to produce food and oxygen.

9- The cassava moth and the cassava plant

Cassava moth intervenes in the process of pollination of this plant. In return, the plant offers protection to moth eggs and feed the larvae once they are born.

10- Mycorrhizae

Mycorrhizae are associations between fungi and the roots of a plant. The plant provides food to the fungus, while the fungus increases the area of ​​nutrient absorption of the plant.

11- Ants and acacias

Ants lay their eggs on the thorns of acacias. In exchange for the protection offered by the trees, the insects protect the acacias of the herbivores.

12- Lichens

Lichens are a case of symbiotic relationship, composed of a fungus and a seaweed. In this relationship, the fungus obtains food through the process of photosynthesis Made by the plant and, in return, protects the algae by providing moisture so that it can survive.

13- Picabueyes and antelopes

As with rhinoceroses, picabueyes perch on antelopes and feed on ticks on their fur.

14- The bumblebee and the black broom

The relation of mutualism between these two species is of pollination.

15- The tarántula and the toad boqui

The toad is fed on parasites that could affect the eggs of the tarantulas. In return, the tarantula allows you to live in your territory.

16- Prawns and fish

Prawns clean ectoparasites on the skin of fish. In this way, they prevent the fish from becoming infected with diseases and obtaining food.

17- Ants and fungi

Ants produce fungi from the leaves of plants and fecal material. Once these fungi grow, the ants partially feed on them.

18- Remoras and sharks

Remoras are small fish that can be seen close to sharks. These animals ingest the remaining debris after the shark has eaten. In this sense, the shark is kept clean and the hind limb is fed.

19- Cows and rumen bacteria

Like bacteria in the human intestine, the bacteria of the rumen inhabit the digestive tract of the cows These bacteria help these mammals in the digestion of certain plants and, in exchange, obtain food.

20- Binding bacteria of nitrogen And plants

Some plants, such as alders, are able to live in areas poor in nitrogen thanks to certain bacteria that help fix this element.

Rainforests of the Sea: Mutualism on Coral Reefs

Coral reefs are home to some of the most diverse ecosystems on the planet. The intricate shapes and bright colors found on reefs can be reminiscent of the Dr. Seuss books that we all read as kids. They are also sometimes called the rainforests of the sea, mostly because coral reefs rival tropical rainforests in biodiversity, but also because of the obvious biological complexities that can be observed on any part of a reef. One of these complexities can be viewed in the form of symbiotic relationships, which occur between all kinds of reef-dwelling (or building!) organisms.

There are three main types of symbiotic relationships found in nature: mutualism, commensalism, and parasitism. In blog posts that I will update over the next few months, I will outline how each of these relationships are prevalent on coral reefs while providing examples of each, how human impact is affecting them, and how this will ultimately affect coral reef ecosystems on a global scale.

The first type of symbiotic relationship, and the main focus of this post, is mutualism. In these kinds of interspecific relationships, both (or all) organisms involved benefit from the interactions. There are numerous examples of mutualism on coral reefs. One is the relationship that cleaner shrimp ( Lysmata anboinensis ) have with many species of larger ‘client’ fish, who come to the shrimp to be cleaned of parasites and dead skin, which the shrimp then eat¹ . If you’ve ever seen Finding Nemo , the character Jacques was actually a cleaner shrimp! This is a prime example of a mutualistic relationship the shrimps benefit because they get food while the fish benefit because they get rid of possibly harmful parasites and dead skin. This relationship is pictured below.

Image 1: L. anboinensis ‘works’ on a yellow-edged moray eel (Gymnothorax flavimarginatus) to rid the fish of parasites and dead tissues. Credit: Jesse Cancelmo

Another example of mutualism on reefs is one that is vital to the health of the reef and all its inhabitants: the relationship that corals have with zooxanthellae. Corals are animals that consist of vast carbonate (limestone) skeletons produced by tiny individual polyps, which comprise the actual animal part of the coral. Zooxanthellae (dinoflagellates that live in symbiosis with many types of invertebrates) live within the polyp tissue and use carbon dioxide and H2 O from the coral to carry out photosynthesis. They in turn provide the coral with sugars, lipids, and oxygen for growth and the continuation of the cycle of cellular respiration² .

You might have heard of something called ‘coral bleaching’ – this is the phenomenon by which corals lose their symbiotic zooxanthellae due to drastically changing ocean conditions (including temperature, salinity, and acidity). Coral bleaching is characterized by white, thin-looking corals as opposed to brown or greenish corals that are fuller in composition (pictured below).

Image 2: Acropora coral experiences bleaching on the Great Barrier Reef. Credit: Prof. Ove Hoegh-Guldberg: Chair, CRTR Coral Bleaching Working Group

Because corals are completely dependent on zooxanthellae, losing this critical relationship is a blow to any reef that experiences bleaching. Bleached coral can recover, but only if zooxanthellae return to the corals in a relatively short amount of time (usually a few days). After this, the coral dies and becomes a part of the extensive skeletal structure of the reef. Although reef growth requires the accumulation of coral carbonate skeleton, infinitely more important is the presence of live coral, which provides many ecological benefits beyond the zooxanthellae.

Figure 1: Mean survivorship of 4 prey fish associated with different habitat treatments (n = 6 for each treatment): 1) healthy, 2) bleached, 3) dead, 4) algal covered, and 5) control (no predator) after being exposed to a predator for 75 h. Mean SE = 6.5%, 4.3%, 4.2%, and 3.7%.³

The very possible continued global bleaching of coral reefs not only threatens corals themselves, but also the many species of fish and other marine creatures that make reefs their home (this in and of itself is an example of mutualism). Reefs serve many roles, including the role of protector from predators for many species. Many predators use contrasting coloration to find prey, and for this reason many prey species have adapted to resemble certain parts of reefs. Since bleaching changes the color of corals, this can make coral-dwellers more susceptible to predation3 . The structural degradation of reefs can also attribute to greater predation rates, since prey species won’t be able to hide in the same nooks and crannies that they have in the past. See Figure 1 for an idea as to how much prey species rely on corals.

Since close to a quarter of marine biodiversity depends on reefs in some way4 , it is vital that their structural and functional integrity remain intact. Reefs provide some of the greatest examples of mutualism in nature, and their existence as a resource for biologists and other researchers remains something worth protecting.

1 Lysmata amboinensis: WAZA: World Association of Zoos and Aquariums

3 Darren J. Coker, Morgan S. Pratchett, Philip L. Munday Coral bleaching and habitat degradation increase susceptibility to predation for coral-dwelling fishes. Behav Ecol 2009 20 (6): 1204-1210. doi: 10.1093/beheco/arp113


Parasitism is another symbiosis relationship. The word parasite comes from the Latin word parasitus, which means to eat another. The word parasitism comes from parasites. Different species in the world lived through interactions. In biology, there is a relationship between symbiosis species where two different species have a parasite and a host (plant or animal). But between these two different species, one species benefits and the other species harms. In parasitism one species benefits and another species harms. The species that benefit is called a parasite. The species from which the parasite collects nutrients and benefits is called the host. The parasite harms the host but does not kill the host (2) & (4).


There are some species in nature that collect nutrients from the host and harm the hos called parasites. Rafflesia, Viscum, Striga Asiatica, dodders, santalum, tapeworms, roundworms, etc. are the parasites. They get food from the body of another living host. Dodders collect food from the host’s body by building its own stem on the trunk of the host tree. It can also cause the death of the host plant. Worms also live in the human body. It absorbs nutrients from the human body and harms humans (1) & (4).

Can a relationship exist that is mutualistic/parasitic/etc. but not considered symbiotic? - Biology

Principles of Ecology

320 Harned Hall

Lecture 15 Symbioses: Mutualism, Commensalism & Parasitism

Overview - Link to Course Objectives

  • Symbiosis, Parasitism and Mutualism
    • Parasitism
    • Mutualism
    • Symbiosis
    • DiffuseMutualism
    • Biological Control
    • Pollination
    • Dispersal Mutualisms
    • Cleaning Mutualisms
    • Defense Mutualisms
    • Bacteria - Aphid Mutualism
    • Lichens Mutualism
    • Plants - MycorrhizaeMutualism
    • Plants - Nitrogen-Fixing Bacteria Mutualism
    • Hard Corals - Algae Mutualism
    • Giant Clam - Algae Mutualism
    • Yeast-DrosophilaMutualism
    • Crab-CoralMutualism
    • Agricultural Mutualisms
      • Ant - Fungus MutualismMutualismMutualismMutualism

      Symbiosis, Parasitism and Mutualism

      • Parasitism is one of the +,- species interactions
      • There is no easy definition that will separate everything biologists consider parasites from herbivores or predators
        • almost never kill the host directly (although some diseases do this, of course)
        • usually live in intimate contact with their hosts (although some insects commonly considered parasites, like ticks and mosquitoes, spend much of their life span not in contact with a host)
        • tend to be much smaller than their hosts so that one host often supports many parasites
        • some parasites have only one species as a host
          • many diseases infect only one or a couple of host species
          • ticks and mosquitoes will bite any warm-blooded animal they find
          • these parasites (many parasitic worms [Platyhelminthes and Nematoda]) have complex life cycles
          • often two different species as hosts (rarely three)
            • often the hosts are not closely related for parasites with complex life cycles
            • schistosomiasis nematode must infect both a freshwater mollusk and a vertebrate to complete the life cycle
              • parasite reproduces asexually in intermediate host
              • some vectors are not affected by parasite and can't be considered hosts, just vehicles to transport the parasite
              • some vectors are also hosts
              • Ectoparasites that remain outside of the host's body
              • Endoparasites that enter the host's body
              • Holoparasites (used for plants only) plants that parasitize other plants and no longer photosynthesize but get all water and food from the host (ex: Dodder, Dutchman's Pipes)
              • Hemiparasites (used for plants only) plants that parasitize other plants for water and minerals, but photosynthesize to make their own food (ex: Mistletoe)
                  • Don't confuse hemiparasites with epiphytes , plants that grow on other plants but do not invade their tissues to steal water and nutrients (ex. many orchids
                  • Parasites may kill (as when a disease kills its host)
                  • Parasites may reduce host fitness through lost growth or lost reproduction due to stress from harboring parasite
                  • Parasites may sterilize the host
                  • Parasites may alter the hosts phenotype
                      • some parasites change the sex of the host
                      • some parasites alter behavior of the host so that the host acts to benefit the parasite (at its own expense)
                      • Come from almost all taxonomic groups
                        • parasitic bacteria. plants, fungi, protists, and animals
                        • Relationship between two organisms that benefits both
                          • mutualisms carry both costs to each partner and benefits as well
                          • mutualisms are favored when the benefits are greater than the costs, so it is the net benefits (or benefit cost ratio) that determine the outcome of these interactions
                          • Obligatory - organisms cannot survive in the absence of the other partner
                          • Facultative - organism can lead an independent existence
                          • one organism may be obligated to the mutualism, while the other can live without its mutualistic partner
                          • Example of asymmetry -
                              • many stony corals do not feed at a rate to sustain themselves when they lose their algal partners
                              • the algal partners can usually grow and reproduce outside of the corals
                              • Mutualism once thought to be among the important interactions among species
                                • Allee and the terrestrial isopods
                                  • Showed that terrestrial isopods (pillbugs or rolly-pollys), which are very susceptible to desiccation, survived longer in groups than when alone when the soil got dry
                                  • Allee effect is still used to indicate an situation in which animals are better able to survive and reproduce in groups than when alone
                                  • interpreted this to mean that organisms often cooperated for mutual benefit
                                    • makes cooperation as important as competition and predation (more negative interactions)
                                    • Competition/predation studies became more common
                                    • Theory predicted that conditions that favored mutualisms were narrow and unlikely to be found in nature.
                                    • important mutualisms identified (mycorrhizae, nodulation, arthropod-bacterial nutritional mutualisms, etc.)
                                    • theory modified to widen the conditions under which mutualism is favored by selection.

                                    Relationship between parasitism and mutualism

                                    • Many parasitic relationships evolve to reduce the cost for the host
                                      • benefits the host in that the parasites do less damage
                                      • benefits the parasite in that there will be more hosts to parasitize if they are not excessively harmed by the parasite
                                      • How do mutualisms begin if the benefits only arise when the partners come together? Were the adaptations serendipitously already there?
                                        • This seems not likely due to the prevalence of mutualisms.
                                        • Plants that attracted the insects to their reproductive structures benefited from the accidental pollinations
                                          • From the accidental beginning, where the plants were mostly harmed by the insects, the elaborate pollination systems (including flowers, floral rewards, specialized animal behaviors, etc.) developed over time to increase the benefits of the interaction to both partners.
                                          • a relationship between individuals of two different species in which individuals of one species lives on or in individuals of the other species
                                          • mutualisms may or may not be symbiotic
                                            • lichen fungi and lichen algae are only found together - symbiotic
                                            • plants and pollinators are only in contact when the pollinator is feeding - not symbiotic
                                            • parasitic tapeworms can only grow and reproduce in the gut of a vertebrate and only leave one host to get to another - symbiotic
                                            • mosquitoes spend as little time on their hosts as possible (for obvious reasons) - not symbiotic
                                            • these are called diffuse because the strength of the connection between any two species is not as strong as when each species has one and only one other species with which it can form a mutualism
                                            • may involve many species
                                              • yeast living together often have mutualisms in which each can feed from the activity of the others present and the interaction may involve three or more species
                                              • the species involved in the mutualism may change from place to place or through time
                                              • some plants have many species as pollinators, including birds, bats, and insects

                                              We can modify the logistic equation to model mutualism, just as we did for competition. The difference this time is that we assume that the presence of a mutualist has the opposite effect that the presence of a competitor did. A mutualist will increase the carrying capacity of the environment, and the size of the effect will increase as the number of mutualists does.

                                              • The equations above do this (notice how close to the Lotka-Volterra equations they are). Each equation is identical to the Lotka-Volterra equation but the sign of the alpha term has been changed to positive. Thus, addition of the mutualist species adds to the total number of individuals that can be sustained in the population (K is supplemented, not reduced as it is in competition).
                                              • These equations can be solved to get a zero-isocline and analyzed in the same fashion as in the competition model.

                                              • the + and - signs indicate the growth rate of each species when the system is in a particular region (the first of the pair is always species 1, the second is always specie 2)
                                                • notice that, in both graphs, the + region is consistent. For instance, all space to the right of K1 is negative for species 1, indicating that in this region the population size of species 1 is too great, it is beyond the carrying capacity, even accounting for the presence of he other species (which increases the populations size in this case).
                                                  • If you go to the notes for the chapter on competition, you will see that the + and - regions are consistent between these graphs and the graphs generated by the Lotka-Volterra equations
                                                  • The Run Away graph on top describes a case in which the zero isoclines do not cross. This means there is no point at which both species are just maintaining their population sizes. In other words, there is no equilibrium point with both species present. What happens, if you follow the vector changes around (see the book), is that, no matter where you begin in this system, you end up with a run-away situation, in which one species always increases the size of another species, which, in turn, increases the size of the first, which increases the size of the second . . . until both species hit infinite population sizes.
                                                  • The Stable graph on the bottom has an intersection point. where both species' growth rates are 0, so that it is an equilibrium point. If you follow a point around, you will see that it is a stable equilibrium point and no matter where you begin, you always end up at the stable point. Thus, we can see that a stable mutualism is possible even with these simple equations.
                                                  • In the Collapsing graph on top, there is no equilibrium point with both species present. If you use the + and - signs to follow a point through time, you will see that, no matter where you start you end up at the origin
                                                    • this means that neither species can exist in this environment, no matter how many of the mutualists are present.
                                                    • this means that this obligate mutualism is unstable, and any change in the population size of either member of the mutualism will mean the collapse of both populations.
                                                    • Note that the book has some more sophisticated models, in which the zero isoclines are not straight line but are curved, and that this opens up the possibility of stable obligate mutualisms
                                                    • this might mean that nature is more complex than our simple models, but I think we should at least explore how things might interact with the simple models before going on to more complicated models.

                                                    Epidemiology is the science that studies disease

                                                    • Infectious diseases are caused by parasites and are the most intensively studies parasite systems (due to their importance to our health)
                                                    • parasites are referred to as pathogens in epidemiology

                                                    Factors in the spread of disease

                                                    • Note that the parasite population is not usually studied, but the number of infected hosts is studied
                                                      • If all parasites are in one host, and it dies, the pathogen population dies, no matter how large it is
                                                      • If a smaller number of parasites are spread into many hosts, the death of a single host will not eliminate the pathogen
                                                      1. S = the density of susceptible hosts (notice that density is usually used here, not total population size)
                                                      2. B = transmission rate (depends on virulence of disease, mode of transmission, and host behavior)
                                                      3. L = the average period during which a host will be infectious
                                                      4. Rp = the replacement rate of infected hosts (note that it is not the R0 of the parasite, as there may be lots of parasites and lots of parasite reproduction in each host) . However, a bit like R0, if Rp is less than 1, the rate of infection is such that there are fewer and fewer infected hosts as time goes on, if Rp is equal to 1 then the number of cases is stable, and if Rp is over 1, then the disease is increasing in incidence

                                                      We can relate these factors with the following equation:

                                                      • The longer the host is infective, the greater the replacement rate of parasitized hosts, so there is pressure on the parasites to keep the host alive (increase L, increase Rp)
                                                      • High transmission rates (large B) leads to greater replacement rate of parasitized hosts, so there is pressure on the parasites to evolve greater rates of transmission (increase L, increase Rp)
                                                      • Given the limited resources of the host, it may not be possible to do both of the above
                                                      • If NT is not constant, an increase in either transmission rate or infectious period will reduce the size of the host population needed to maintain the parasite
                                                      • If NT is constant, then an increase in one parameter (either transmission rate or infectious period) will lead to a decrease in the other parameter (in other words, an increase in transmission rate will reduce the infectious period and vice versa)

                                                      Evolution and Mutualism/Parasitism

                                                      • Evolution of parasitism and mutualism are excellent examples of the process of Coevolution
                                                        • Coevolution is the process of evolutionary change in two species in which each changes in response to change in the other species
                                                        • Coadaptation is a characteristic of an organisms that is involved in the mutualism/parasitism by interacting with some feature of the other partner
                                                          • an example is the communication that goes on between roots and nodulating bacteria
                                                          • Coadaptations need not be the product of coevolution
                                                            • Serendipity - good fortune due to chance - can also bring together two organisms that already have features that make their mutualism possible
                                                            • Stable mutualisms must prevent cheating by a partner (getting benefit, bearing no cost)
                                                            • Coadaptation often due to arms race type of coevolutionary changes in host and parasite
                                                            • Parasites differ with respect to their host specialization
                                                              • Monophagous parasites attach a single species of host
                                                              • Polyphagous parasites attack several species of hosts (usually they are related)

                                                              The Impact of Parasites:

                                                              • Host defenses
                                                                • Cellular Defense Reactions
                                                                  • Encapsulation of parasite's cells (often reproductive cells) by the host so that they are non-functional
                                                                  • Cell surface changes
                                                                    • Change the marker molecule and the parasite may not recognize the host
                                                                    • Often can see the effect of an addition of the parasite to the host population as an epidemic (outbreak) of a disease
                                                                    • Difficult to remove the parasite from a natural population and so it can be difficult to do field experiments with parasitic systems
                                                                        • If this were not so, we would have performed many such removals in trying to cure us and our crops and livestock of disease
                                                                        • basis is the proportion of susceptible hosts
                                                                          • susceptible hosts become non-susceptibles after infection, as immunity's memory system makes a second infection unlikely
                                                                          • After an outbreak, enough hosts become immune to drop Rp below 1, so the disease declines in the population
                                                                          • As disease prevalence falls, new individuals entering the population (births and migration from populations without the parasite) boost the proportion of susceptibles
                                                                          • When this proportion is high enough to boost Rp over 1, another outbreak begins, starting the cycle over again
                                                                            • Can you see why this cycling is most apparent in diseased that affect children?
                                                                            • Rinderpest in Southern Africa - virus with wide host range (large, grazing mammals)
                                                                              • Buildup of host (cattle) after establishment of European-style ranching
                                                                              • Outbreak of parasite after introduction of diseased cattle from Southeast Asia caused decline in cattle
                                                                                • also led to loss of natural populations of other hosts
                                                                                  • Decline in wild populations of large grazing animals (antelopes, gnu, etc.) lead to:
                                                                                      • change in vegetation over wide areas
                                                                                      • reduction of tsetse fly population, which feed on large mammals
                                                                                      • White-tail deer and Parelaphostrongylus tenuis
                                                                                        • White-tail deer are tolerant
                                                                                        • Other cervids (moose, other deer like the mule deer, pronghorn) are harmed
                                                                                        • Evolution of resistance to antibiotics an example of the evolutionary potential of parasites
                                                                                        • Virulence (transmission rate and infectious period) may vary through time
                                                                                          • Rabbits and Myxomatosis
                                                                                            • Less virulent strain of virus evolved
                                                                                            • When alone, less virulent strain meant that rabbits would live longer, infect more bloodsucking insects (vector)
                                                                                            • after time, Myxomatosis became a non-lethal disease and now a second virus, Calcivirus, is being used
                                                                                            • Attempt to reduce the population of a pest to an acceptable level through manipulation of the population ecology of that pest
                                                                                              • Note that it says reduction and not elimination of the pest
                                                                                              • elimination may sometimes occur buy the usual outcome is the reduction of host to lower population levels than without the parasite
                                                                                              • Herbivores and predators are also used
                                                                                              • sterile male release also used (screw worm)
                                                                                              • Death rate strategies
                                                                                                • Rabbits and Myxomatosis
                                                                                                • Poses potential problems as the disease might jump to new hosts in the new environment and kill non-target species
                                                                                                • Sterile male programs
                                                                                                • Med fly and Screw worm programs

                                                                                                Examples of Mutualisms

                                                                                                • Pollinator may get:
                                                                                                  • Food (nectar, pollen- high energy or high protein food)
                                                                                                  • Mating advantage - some bees get scent molecules
                                                                                                  • Nesting materials - some bees get wax for their nests
                                                                                                  • Efficiency of pollen transfer (compared to wind)
                                                                                                  • Mixing of pollen from many plants and prevention of inbreeding
                                                                                                  • any animal that visits the flower regularly may be a pollinator

                                                                                                  May be a very "tight", highly coevolved relationship or a diffuse relationship

                                                                                                  • Examples of diffuse systems
                                                                                                    • Many flowers in the fields in Tennessee are visited by more that a dozen species of insect, all of which may act as pollinators (I have seen 10+ species of insect visiting a flowering fruit tree at the same time)
                                                                                                    • Orchids and pollinators
                                                                                                      • many orchids are pollinated by a single species of insect
                                                                                                      • flowers of orchids are often shaped so that only the correct insect can get to the nectar and so will carry the pollen
                                                                                                      • there are many species of fig - they produce many flowers enclosed in a capsule (we call the capsule and its contents a fig)
                                                                                                      • each has its own species of wasp (called Agaonid wasps)
                                                                                                      • the female wasp lives all of its larval life in fig and only spends enough time out of one as an adult to disperse to the next fig, where she will deposit her eggs and never leave (only its progeny will)
                                                                                                      • males never leave the fig in which they hatched, grew as larvae, and pupated
                                                                                                      • fertilize females in same fig and die there, never having left it
                                                                                                      • the fig must supply food for its wasps or it will not produce a new generation
                                                                                                      • wasps must not overexploit the resource or they will eat the fig and it will never produce the next generation of fig plants
                                                                                                      • neither species can enter a new environment without the other
                                                                                                      • similar to fig story - each species of yucca is pollinated by a single specie of moth which lives only on the species of yucca that it pollinates

                                                                                                      Some plants and some animals cheat

                                                                                                      • some animals may take nectar but do not carry pollen
                                                                                                        • some insects are unable to get to the bottom of deep, vase-like flowers but simply drill through the base of the flower to steal nectar
                                                                                                        • some plants have flowers that look and smell like females of insects. They attract the males, who mate with the flower and carry away pollen
                                                                                                        • Fruits are plant rewards for animal dispersal of seeds
                                                                                                        • Seeds often pass through the guts of dispersers without harm
                                                                                                          • some seeds even benefit from this by being deposited with the manure as a fertilizer
                                                                                                          • some seeds use the passage as a signal to germinate and will not do so without this
                                                                                                          • some plants protect the seed with toxins while making the fruit palatable
                                                                                                            • peach seeds (pits) are full of cyanide
                                                                                                            • make fruit apparent to dispersers (advertisements)
                                                                                                            • green fruit often contain same toxins as other part of plant to stop herbivory
                                                                                                              • when ripe, color change signals readiness in that the fruit has:
                                                                                                                • lost it toxins
                                                                                                                • been stocked with sugars
                                                                                                                • one species gets food by removing (and eating) ectoparasites of another
                                                                                                                • partner loses its parasites without having to clean itself
                                                                                                                  • happens on reefs where cleaner shrimp clean parasites from fish at "cleaning stations"
                                                                                                                  • also on reefs, cleaner fish perform same function as shrimp
                                                                                                                  • oxpecker birds eat parasites from outside of large herbivores (cattle, antelope, rhinoceros)
                                                                                                                    • although they keep the ticks, etc. off, this may not be a mutualism, as the oxpecker will peck a vulnerable area (often an ear) and drink blood when parasites are not available
                                                                                                                    • one species gets food and/or shelter from another species
                                                                                                                    • other partner gets protection from being eaten
                                                                                                                      • Ant-Acacia system
                                                                                                                        • Bull Thorn Acacia provides:
                                                                                                                          • place for ants (Pseudomyrmex) to live in swollen base of acacia thorns (hence the name bull-thorn)
                                                                                                                          • food for ants in form of special extension of leaves call Beltsian bodies
                                                                                                                          • other insect herbivores
                                                                                                                          • large, vertebrate herbivores (including you, if you happen to lean on the tree)
                                                                                                                          • Some grasses are infected with fungi (Clavicepts and other Ascomycetes) - long though to be parasitic but the fungi are the source of alkaloids
                                                                                                                          • the alkaloids are protection from herbivory as they are toxic and bitter
                                                                                                                          • some evidence that infected plants grow faster and produce more seed.

                                                                                                                          Bacteria - Aphid, Leaf Hopper Mutualism

                                                                                                                          • Aphids and leaf hoppers feed on sugary sap sucked directly from the phloem tubes of plants
                                                                                                                            • sap is a poor diet that is high in sugars, low in amino acids
                                                                                                                            • insects have essential amino acids, just like us, and so they cannot live on this diet without help
                                                                                                                            • Bacteria receive sugars from plant via the aphid and supply the aphid with amino acids
                                                                                                                            • Bacteria also receive easily-made amino acids from insect and transform them into essential amino acids that the insect cannot make
                                                                                                                            • In one case, the leaf hopper does not excrete the uric acid it produces as its nitrogenous waste but recycles it to the yeast, which use it in amino acid synthesis
                                                                                                                            • In the same insect, the yeast synthesize proteins that are stored in the eggs and, without these proteins, the eggs will not produce viable zygotes when fertilized
                                                                                                                            • they also occur in some beetles (Anobiid Beetles) that live in dead wood (called powder-post beetles because of the wood dust from their boring activities)
                                                                                                                            • Some insects called Lacewings (Neuroptera) are important in biological control because their larvae eat aphids and planthoppers but the adults of some species feed on plant sap and have yeast in their guts that provide them with required amino acids and lipids
                                                                                                                            • Many fungi are lichenized, each one needs a particular species of algae
                                                                                                                              • each algae species usually can form a lichen with several different species of fungi
                                                                                                                              • because the fungus is the unique partner in each lichen, it is the fungal name that becomes the lichen's name

                                                                                                                              Plant - Mycorrhizae (and some bacteria)

                                                                                                                              • Very common and very important mutualism - these fungi can be 50% of the microbial biomass in soils
                                                                                                                                • two important types:
                                                                                                                                  • Ectomycorrhizae - many species of both Ascomycota (ascus-forming fungi) and Basidiomycota (club-spored fungi), the two largest fungal groups - many common mushrooms are the reproductive structures of ectomycorrhizal fungi
                                                                                                                                    • wrap hyphae around roots, do not penetrate cell walls of plant cells
                                                                                                                                    • hosts are trees (many conifers) in temperate or boreal systems
                                                                                                                                    • hyphae have no walls (septae), so the entire mycelium (all the thread-like hyphae) are essentially a single cell (this condition is called coenocytic).
                                                                                                                                    • hyphae penetrate the cell walls and split into lots of bifurcations that end in vesicles (swollen tips), but the hyphae do not penetrate the cell membrane, which folds inward to accommodate the fungal growth
                                                                                                                                    • almost any plant that does not have an ectomycorrhizal association will have a VAM association (the majority of plants by far)
                                                                                                                                    • have BLO's inside their hyphae - first called Bacteria-like organelles, now known to be intercellular bacteria - role in the system not known at this time
                                                                                                                                    • minerals from absorptive power of fungi
                                                                                                                                      • hyphae of fungi increase the absorptive area of roots by penetrating the soil much more finely than the roots can
                                                                                                                                      • growth rate and reproduction of plants often much lower if mycorrhizae are removed
                                                                                                                                      • all Orchids have important pollinator mutualisms with insects (see above) and also important fungal mutualisms
                                                                                                                                      • orchid seeds are tiny and have little stored resources (fats, carbohydrates, proteins) for the germinating embryo
                                                                                                                                      • Orchid mycorrhizae in soil (or on surface of a plant for epiphytic orchids) penetrate the seed coat and trigger germination of the seed, then supply the young plant with sugars and proteins until it becomes photosynthetic and can return the favor
                                                                                                                                      • some orchids are non-photosynthetic and the mycorrhizae continue to supply sugars and proteins that they get by penetrating the plants the orchid is growing on - in this case the fungus is a parasite of one plant (the tree) and a mutualist of another (the orchid) at the same time.

                                                                                                                                      Plants - Nitrogen-Fixing Bacteria

                                                                                                                                      • Nitrogen is a form useable by plants (nitrate, nitrite, or ammonium) is the product of the metabolism of other organisms
                                                                                                                                        • N2 is plentiful in atmosphere but useless to plants
                                                                                                                                        • the process of making N2 into organic nitrogen (as the above forms of N are collectively called) takes lots of energy
                                                                                                                                        • bacteria (Azotobacter, Azobacter, some Pseudomonas species, some blue-green algal species) are free-living microbes that can fix nitrogen
                                                                                                                                          • the bacteria are all anaerobes and live in regions of the soil where oxygen has been depleted (see section on coadaptation and leghemoglobin below for why this is so)
                                                                                                                                          • Lack of nitrates (and derived compounds) often limits plant growth in terrestrial ecosystems
                                                                                                                                          • Ability to produce organic N locally is a great advantage in nitrogen-poor soils
                                                                                                                                          • many plants in the Fabaceae (also called the Leguminosae - the pea family that includes peas, beans, clover, alfalfa, honey locust trees, and many more trees) and other families can nodulate
                                                                                                                                          • Rhizobium is the genus of bacteria that participate in nodulation
                                                                                                                                          • Nodules provide bacteria with a place to live and an environment conducive to their growth
                                                                                                                                          • Plant responds to chemical signals produced by bacteria
                                                                                                                                            • secretes chemical attractants for the bacteria, which migrate to root and enter it
                                                                                                                                            • presence of the bacteria and their secretions promotes cell proliferation by plant to make the nodule
                                                                                                                                            • supply photosynthate to bacteria for growth and for the expense of fixing N
                                                                                                                                            • must also maintain the proper, oxygen-depleted environment for fixation
                                                                                                                                              • nitrogenase, the enzyme that catalyzes the fixation, is sensitive to the presence of oxygen
                                                                                                                                                • oxygen fits into its active site as well (or even better) than does nitrogen, so it poisons the process if it is present
                                                                                                                                                • oxygen is soaked up by the presence of a compound, Leghemoglobin , that binds to oxygen
                                                                                                                                                  • Leghemoglobin is related to our hemoglobin, both through structure and ancestry
                                                                                                                                                  • the protein portion is produced by the plant from genes in its nucleus
                                                                                                                                                  • the heme portion is produced by the bacterium with enzymes encoded by genes on its chromosome
                                                                                                                                                  • pea family plants all grow without nodules (but more slowly)
                                                                                                                                                  • bacteria grow in soil without pea plants (but much more slowly)
                                                                                                                                                  • Corals get photosynthate from algae
                                                                                                                                                  • algae get minerals extracted from sea by animals
                                                                                                                                                    • free-floating algae are "trapped" in the water drop in which they float
                                                                                                                                                      • only get nutrients that diffuse into their neighborhood and diffusion is a very slow process
                                                                                                                                                      • they extract nutrients from many gallons of water each day, not just from the drop in which they are floating
                                                                                                                                                      • waters surrounding reef are usually very clear - indicating that they have little algal growth (low productivity)
                                                                                                                                                      • reefs are as productive as tropical rain forests, among the most productive systems on earth
                                                                                                                                                      • Algae can leave when conditions not right (bleaching of coral)
                                                                                                                                                      • Coral can feed by predation on plankton (but growth is slow or even negative)
                                                                                                                                                      • Clam gets photosynthetic output of algae
                                                                                                                                                      • algae get minerals absorbed by clam and protection from herbivores

                                                                                                                                                      Yeast- Drosophila Mutualism

                                                                                                                                                      • Yeast need to disperse from habitat patch to patch
                                                                                                                                                        • Yeast spores are not resistant to desiccation so they must be carried
                                                                                                                                                        • plants often low in protein, which are needed for making eggs as adults (even when eaten by larvae)
                                                                                                                                                        • most yeast grow in dead plant material
                                                                                                                                                          • yeast are much higher in protein than the plant tissue they eat and so are high quality food for insects
                                                                                                                                                          • 10-20 species of fly, all found only in cacti
                                                                                                                                                          • 20-30 species of yeast, most found only in cacti
                                                                                                                                                          • mutualism is diffuse but obligatory
                                                                                                                                                          • Flower Beetles (Nitulid beetles) and yeast have a mutualism very similar to Drosophila and yeast
                                                                                                                                                            • the beetles carry yeast from flower to flower
                                                                                                                                                              • the yeast use the flower for food
                                                                                                                                                              • the beetles eat the yeast

                                                                                                                                                              Coral-Crab Mutualism

                                                                                                                                                              • Hard corals need sunlight (see the coral-algae mutualism above)
                                                                                                                                                                • Overgrowth of corals by seaweeds (macroalgae) can shade them and kill them.
                                                                                                                                                                  • Some corals (Oculina arbuscula is an example) avoid overgrowth because an herbivorous crab (Mithrax forceps) forages on the algae.
                                                                                                                                                                  • The crab gets not only the algae as food. It lives in the coral and avoids predation as a result. So the coral is not just food, it is a protector.

                                                                                                                                                                  Agricultural Mutualisms

                                                                                                                                                                  • These are mutualisms in which an animal cultivates a fungus by providing a place and the plant material that is the fungus' food and eats the fungus
                                                                                                                                                                  • The advantage for the animal is that the fungus is higher quality food (more protein, less indigestible carbohydrate, fewer secondary chemicals, more vitamins) than the plant material
                                                                                                                                                                  • the advantage for the fungus is that it is provided food and, in some case, a controlled environment in which to grow

                                                                                                                                                                  Ant - Fungus Mutualism

                                                                                                                                                                  • Leaf Cutter Ants cut pieces of vegetation and carry it back to their nest
                                                                                                                                                                    • Chew the plant into a mush on which the fungus grows
                                                                                                                                                                    • Ants eat the fungus, not the plant that they cut
                                                                                                                                                                    • grows best at temperature maintained in the center of the nest
                                                                                                                                                                    • fungus is a monoculture - whereas most fungi must live with other, competing species of fungi

                                                                                                                                                                    Termite - Fungus Mutualism

                                                                                                                                                                    • Termites are famous for their mutualistic association with protists that reside in their gut
                                                                                                                                                                      • The termites cannot digest the wood they eat but the protists can, so the beetles eat the wood but the protists digest it and the beetles digest the protistans
                                                                                                                                                                      • 75% of all termites have no protistan mutualists and some of these can produce cellulase, the enzyme needed to digest wood, themselves
                                                                                                                                                                      • Not all termites feed directly on wood
                                                                                                                                                                        • Some termites farm fungi in their nests, where the fungi digest the wood and the termites eat the fungi
                                                                                                                                                                        • The termites carry the fungi to new nests and will die if the fungal mutualist is lost (which can happen if another fungus or a bacterium contaminates the nest

                                                                                                                                                                        Beetle - Fungus Mutualism

                                                                                                                                                                        • Bark beetles bore into tree trunks and excavate tunnels under the bark or into the woody portions of the trunk
                                                                                                                                                                          • Some attack live trees and some bore into fallen trees
                                                                                                                                                                          • Those that attack living trees can cause the death of the tree
                                                                                                                                                                          • These beetles have special pockets on the surface of the exoskeleton which carry fungus from tree to tree
                                                                                                                                                                          • food, as fungi digest the tree and are, in turn, eaten by the beetles and their larvae
                                                                                                                                                                          • protection from toxic secondary chemicals found in the tree trunks
                                                                                                                                                                          • Some trees have resins (think of pine trees) or latex in channels which, when the beetles tunnel into them, flood the beetle's tunnels (also called galleries) and kill them. The fungi can seal off the tunnels and protect the beetles
                                                                                                                                                                          • Transportation from tree to tree
                                                                                                                                                                          • The tunnels, which penetrate the trunk and make the tree available as food for the fungi
                                                                                                                                                                          • Ambrosia beetles attack living tree, but do not kill them
                                                                                                                                                                          • Living in the tunnels has resulted in some unusual behaviors in these beetles
                                                                                                                                                                            • The adults tunnel out nurseries for their larvae and feed them on the fungus in their nursery chambers
                                                                                                                                                                            • inbreeding (sib-mating) as a normal means of reproduction
                                                                                                                                                                            • haplodiploidy in many of the ambrosia beetles (note that the evolution of this reproductive mode has occurred several times, indicating that it is not just an accident that it occurs in these tunneling beetles)
                                                                                                                                                                            • The pockets supply secretions to feed the fungus and secretions that kill bacteria and mold (another type of fungus) to keep their fungal cultures from contamination

                                                                                                                                                                            Snail-Fungus Mutualism

                                                                                                                                                                            • Littorina is a snail that crawls over the stem and leaves of Spartina, marsh cord grass.
                                                                                                                                                                            • Spartina is the dominant species in some areas within salt marshes worldwide and salt marshes are of great economic importance for their fish and for their ability to remove toxins from human wastes carried into estuaries by rivers
                                                                                                                                                                            • The snails do not feed on the Spartina but scrape the surface
                                                                                                                                                                            • After scraping the surface, they deposit fungal spores
                                                                                                                                                                            • The spores germinate and feed on the damaged plant tissue
                                                                                                                                                                            • The snails then eat the fungus
                                                                                                                                                                            • Aphids are protected by ants
                                                                                                                                                                            • Ants get sweet plant sap from aphids
                                                                                                                                                                            • Ants are like ranchers, as they move the aphids from place to place on the plant to take advantage of where most sap is available
                                                                                                                                                                              • So, considering the Ant-Aphid mutualism and the Agricultural mutualism, it appears that we did not discover either farming or ranching, or, if we did, we did not discover it first.
                                                                                                                                                                              • by the way, not only do insects farm and ranch, but they are bakers as well.
                                                                                                                                                                              • Some bee species feed their larvae on pollen, but not before it has been mixed with fungi and bacteria and allowed to ferment (like a baker allowing the bread to rise)
                                                                                                                                                                                • the fermented mixture is referred to as "bee bread"
                                                                                                                                                                                • Situations in which one species benefits from the presence or activity of another species, but the other species gains no benefit nor suffers any harm
                                                                                                                                                                                  • commensal organisms might evolve into either parasites or mutualists
                                                                                                                                                                                  • when one organism attaches itself to another as a means of dispersal
                                                                                                                                                                                  • common way to disperse seeds, animals not harmed
                                                                                                                                                                                    • small animals hitchhike on larger animals
                                                                                                                                                                                    • Bird - Pollen mite
                                                                                                                                                                                      • when birds drink from a flower, pollen mites (feeding on the pollen in the flower) jump on their beaks and nestle into their nostrils
                                                                                                                                                                                      • mites jump off at next flower without harming bird
                                                                                                                                                                                      • Can happen after the burrow is abandoned
                                                                                                                                                                                        • many vertebrates live in burrows made by other species
                                                                                                                                                                                        • Clams in worm burrows on mudflats
                                                                                                                                                                                          • Clams are found no where else, so this is obligate for them
                                                                                                                                                                                          • No evidence that the host worm benefits or is harmed by presence of clam

                                                                                                                                                                                          Silliman, B. R. and Y. Newell. 2003. Fungal farming in a snail. Proceedings of the National Academy of Sciences of the USA 100:643-648

                                                                                                                                                                                          Silliman, B. R. and J. C. Zieman. 2001. Top-down control on Spartina alterniflora production by periwinkle grazing in a Virginia salt marsh. Ecology 82:2830-2845

                                                                                                                                                                                          Parasitism, Host, Host Range, Complex Life Cycle, Definitive Host, Intermediate Host, Vector, Reservoir, Ectoparasite, Endoparasite, Holoparasite, Hemiparasite, Epiphyte, Mutualism, Obligatory Mutualism, Facultative Mutualism, Allee effect, Symbiosis, Diffuse Mutualism, Epidemiology, Pathogen, S (Susceptible Host), B (Transmission rate), L (Infectious Period), Rp (Replacement Rate of Infected Hosts), NT (Threshold Population Size of Susceptible Hosts), Critical Density, Coevolution, Coadaptation, Serendipity, Arms Race, Monophagous Parasite, Polyphagous Parasite, Host defense, Cellular Defense Reaction, Immune Response, Epidemic, Rinderpest, Apparent Competition, Biological Control, Pollination, Cheating, Dispersal Mutualism, Cleaning Mutualism, Defense Mutualism, Beltsian Body, Bacterocyte, Lichen, Mycorrhizae, Ectomycorrhizae, Vesicular-Arbuscular Mycorrhizae, Orchid Mycorrhizae, Nitrogen-Fixing Bacteria, Leghemoglobin, Ambrosia Beetle, Commensalism , Phoresy