CHAPTER OVERVIEW 17: Mutualism and Commensalism Learning Objectives Introduce and explore the types of mutualisms and commensalisms Explore theories that explain the evolution of mutualisms Discuss hypotheses regarding the maintenance of mutualistic relationships 17.1: Introduction 17.2: Types of Mutualisms 17.3: Evolution of Mutualisms 17.4: Maintenance of Mutualisms 17.5: Types of Commensalisms Summary A commensal relationship occurs when one species benefits from a close prolonged interaction, while the other neither benefits nor is harmed. Commensal relationships come many forms including: phoresis, inquilinism, and metabiosis. A mutualism occurs when two species benefit from their interaction, and can be generalized into three types: resource-resource, serviceresource, and service-service. Many mutualisms are thought to have evolved from antagonistic interactions, such as parasitehost relationships. Reciprocal evolutionary responses are most likely important to the evolution of symbiotic mutualisms, like some plant-pollinator interactions, and may be important mechanisms for diversification, though evidence for this is mixed. The maintenance of mutualisms can be undermined by cheating, however, the destabilizing effect of cheating can be minimized by host sanctioning. 17: Mutualism and Commensalism is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
A commensal relationship occurs when one species benefits from a close prolonged interaction, while the other neither benefits nor
is harmed. Birds nesting in trees provide an example of a commensal relationship (Figure
presence of the nest among its branches. The nests are light and produce little strain on the structural integrity of the branch, and
most of the leaves, which the tree uses to get energy by photosynthesis, are above the nest so they are unaffected. The bird, on the
other hand, benefits greatly. If the bird had to nest in the open, its eggs and young would be vulnerable to predators. Many potential
commensal relationships are difficult to identify because it is difficult to prove that one partner does not derive some benefit from
: The southern masked-weaver is starting to make a nest in a tree in Zambezi Valley,
Zambia. This is an example of a commensal relationship, in which one species (the bird) benefits, while
the other (the tree) neither benefits nor is harmed. "African Masked Weaver" by Hanay is licensed under
A mutualism occurs when two species benefit from their interaction. For example, termites have a mutualistic relationship with
protists that live in the insect's gut (Figure
a). The termite benefits from the ability of the protists to digest cellulose.
However, the protists are able to digest cellulose only because of the presence of symbiotic bacteria within their cells that produce
the cellulase enzyme. The termite itself cannot do this: without the protozoa, it would not be able to obtain energy from its food
(cellulose from the wood it chews and eats). The protozoa benefit by having a protective environment and a constant supply of food
from the wood chewing actions of the termite. In turn, the protists benefit from the enzymes provided by their bacterial
endosymbionts, while the bacteria benefit from a doubly protective environment and a constant source of nutrients from two hosts.
Lichen are a mutualistic relationship between a fungus and photosynthetic algae or cyanobacteria (Figure
produced by the algae provides nourishment for both organisms, whereas the physical structure of the lichen protects the algae
from the elements and makes certain nutrients in the atmosphere more available to the algae. The algae of lichens can live
independently given the right environment, but many of the fungal partners are unable to live on their own.
: (a) Termites form a mutualistic relationship with symbiotic protozoa in their guts, which allow both organisms to
obtain energy from the cellulose the termite consumes. (b) Lichen is a fungus that has symbiotic photosynthetic algae living in
close association. (credit a: modification of work by Scott Bauer, USDA; credit b: modification of work by Cory Zanker)
Contributors and Attributions Samantha Fowler (Clayton State University). Original content by e119a8aafbdd).
University), Rebecca Roush (Sandhills Community College), James Wise (Hampton OpenStax (CC BY 4.0; Access for free at https://cnx.org/contents/b3c1e1d2-83...4-
17.1: Introduction is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts. 19.4: Community Ecology by OpenStax is licensed CC BY 4.0.
Resource-resource relationships Mutualistic relationships can be thought of as a form of "biological barter" (Ollerton, 2016). For example, in mycorrhizal associations between plant roots and fungi, with the plant providing food resources (ie, carbohydrates) to the fungus in return for other important nutrients (eg, nitrogen and phosphorous). Other examples include rhizobia bacteria that fix nitrogen for leguminous plants (family Fabaceae) in return for energy-containing carbohydrates (Denison & Kiers, 2004).
A few birds are perched, eating ticks off of various body parts of an impala standing in a field.
: The red-billed oxpecker eats ticks on the impala's coat, in a cleaning symbiosis. Photograph by Muhammad Mahdi Karim.
Service-resource relationships are common. Three important types are pollination, cleaning symbiosis, and zoochory. In pollination, a plant trades food resources in the form of nectar or pollen for the service of pollen dispersal. Cleaning symbioses are carried out by Phagophiles, animals that feed on ectoparasites, thereby providing anti-pest service, as in cleaning symbiosis. Elacatinus and Gobiosoma, genera of gobies, feed on ectoparasites of their clients while cleaning them (Soares et al., 2008). Zoochory is the dispersal of the seeds of plants by animals. This is similar to pollination in that the plant produces food resources (for example, fleshy fruit, overabundance of seeds) for animals that disperse the seeds (service). Plants may advertise these resources using color (Lim & Burns, 2021) and a variety of other fruit characteristics. Another example is ant protection of aphids, where the aphids trade sugar-rich honeydew (a by-product of their mode of feeding on plant sap) in return for defense against predators such as ladybugs.
: Ocellaris clownfish and Ritter's sea anemones live in a mutual service-service symbiosis, the fish driving off
butterflyfish and the anemone's tentacles protecting the fish from predators. Photograph by Jan Derk is available in the public
Strict service-service interactions are very rare, for reasons that are far from clear (Ollerton, 2006). One example is the relationship between sea anemones and anemone fish in the family Pomacentridae: the anemones provide the fish with protection from
predators (which cannot tolerate the stings of the anemone's tentacles) and the fish defend the anemones against butterflyfish (family Chaetodontidae), which eat anemones. However, in common with many mutualisms, there is more than one aspect to it: in the anemonefish-anemone mutualism, waste ammonia from the fish feeds the symbiotic algae that are found in the anemone's tentacles (Porat & Chadwick-Furman, 2004; Porat & Chadwick-Furman, 2005). Therefore, what appears to be a service-service mutualism in fact has a service-resource component. A second example is that of the relationship between some ants in the genus Pseudomyrmex and trees in the genus Acacia, such as the whistling thorn and bullhorn acacia. The ants nest inside the plant's thorns. In exchange for shelter, the ants protect acacias from attack by herbivores (which they frequently eat when those are small enough, introducing a resource component to this service-service relationship) and competition from other plants by trimming back vegetation that would shade the acacia. In addition, another service-resource component is present, as the ants regularly feed on lipid-rich food-bodies called Beltian bodies that are on the Acacia plant (Palomar College, 2019). References Denison, R.F., & Kiers, E.T. (2004). Why are most rhizobia beneficial to their plant hosts, rather than parasitic. Microbes and Infection, 6(13), pp. 1235-1239. doi:10.1016/j.micinf.2004.08.005. PMID 15488744. Soares, M.C., Côté, I.M., Cardoso, S.C., & Bshary, R. (2008). The cleaning goby mutualism: A system without punishment, partner switching or tactile stimulation. Journal of Zoology, 276(3), pp. 306-312. doi:10.1111/j.1469-7998.2008.00489.x. Lim, G., & Burns, K.C. (2021). Do fruit reflectance properties affect avian frugivory in New Zealand? New Zealand Journal of Botany, pp. 1-11. doi:10.1080/0028825X.2021.2001664. ISSN 0028-825X. S2CID 244683146. Ollerton, J. (2006). 'Biological barter': Interactions of specialization compared across different mutualisms. In Waser, N.M., & Ollerton, J. (Eds.), Plant-pollinator interactions: From specialization to generalization (pp. 411-435). University of Chicago Press. Porat, D., & Chadwick-Furman, N.E. (2004). Effects of anemonefish on giant sea anemones: Expansion behavior, growth, and survival. Hydrobiologia, 530(1-3), pp. 513-520. doi:10.1007/s10750-004-2688-y. S2CID 2251533. Porat, D., & Chadwick-Furman, N.E. (2005). Effects of anemonefish on giant sea anemones: Ammonium uptake, zooxanthella content and tissue regeneration. Mar. Freshw.Behav. Phys., 38, pp. 43-51. "Swollen Thorn Acacias". www2.palomar.edu. Retrieved 22 February 2019. Contributors and Attributions This chapter was written by Aaron Howard with text taken from the following CC-BY resources: Mutualism (biology) by Wikipedia, the free encyclopedia 17.2: Types of Mutualisms is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
Evolution of Mutualisms Many mutualisms are thought to have evolved from antagonistic interactions. Several studies have determined ecological or evolutionary conditions driving transitions from mutualism to antagonism (mutualism breakdown) (Kiers et al., 2010; Sachs & Simms, 2000), yet limited theory has been developed to mechanistically explain the evolutionary transitions from antagonism to mutualism (de Mazancourt et al., 2001; deMazancourt et al., 2005). Models of virulence predict evolution of reduced antagonism, perhaps toward mutualism, in cases of parasitism where host fidelity is high and availability of alternate hosts is low (Yamamura, 1993; Yamamura, 1996). In these models, host fidelity is achieved when lineages of parasites and their host are tightly linked through vertical transmission from parent to offspring.
Compelling evidence for the `virulence theory' comes from interactions involving microbial parasites (Weeks et al., 2007; Sachs et al., 2014). For example, Wolbachia are endosymbiotic bacteria that live inside the cells of their invertebrate hosts. They are transmitted directly from mother to offspring, and spread through populations by manipulating the reproduction of their hosts. The most common reproductive manipulation responsible for the spread of these bacteria, called "cytoplasmic incompatibility," arises when infected males mate with uninfected females, resulting in fewer offspring than normal. There are fitness costs for the hosts associated with Wolbachia infections, most commonly involving a reduction in egg production. The virulence theory predicts and evidence suggests that there is selection for the bacteria to evolve a more benign lifestyle, changing the bacterium from being parasitic to more mutualistic, where Wolbachia-infected hosts have higher rates of egg production than their uninfected counterparts (Weeks et al., 2007).
Reciprocal evolutionary responses are most likely important to the evolution of symbiotic mutualisms, and subsequent diversification may be the result of the mutualism improving niche width, population size, or transition into adaptive zones (Hembry et al., 2014). However, with the exception of plant-pollinator interactions, it is unclear how important mutualistic coevolution is as a driving force of diversification, especially as compared to the well-established mechanisms associated with competitive and antagonistic coevolution.
Plant-pollinator interactions are powerful tools of evolution because pollinators transport gametes (via pollen) between flowers. Plant-pollinator relationships are thought to be critical to the historical diversification of angiosperm flowers. In fact, up to 25% of plant speciation events could be as a result of interactions with pollinators (van der Niet & Johnson, 2012).
The obligate pollinating seed-predation mutualisms of the yucca and yucca moth and fig and fig wasps are attributed to coevolution
diversification because the intimacy of the association may prevent species from making phylogenetically drastic switches to new
partners. Interacting with a distant relative of your partner may not be an option if coevolution has created incompatibilities in
specialized traits required for the interaction (Figure
). For instance, if laying eggs into yucca flowers requires a particular
complement of ovipositor traits and moth behaviors, we might predict to find host switches only between closely related yuccas.
Initial analyses of yucca and yucca moth phylogenies suggest that the trees are somewhat congruent, although there have been at
least two instances of moths switching hosts to quite distantly related yuccas (Pellmyr, 2003). The interaction between yuccas and
yucca moths is clearly one that is highly specialized and coevolved, yet we do not find a phylogenetic pattern of perfect matching
: Comparison of host and parasite phylogenetic trees. The dotted lines indicate host associations of the parasites. a)
Matching speciation events between host and parasite show a strict pattern of cospeciation. b) Host switches to distant relatives are
shown by the crossing lines. Some parasites use closely related hosts, but most have jumped to a distant relative. Source: Segraves, 2010.
However, there is also evidence opposing the primacy of mutualistic coevolution in these relationships. Figs have been shown to be
successfully pollinated regardless of pollinator species (Moe & Weiblen, 2012) and pollinator host-switch may be more frequent
than co-speciation events (Wang et al., 2021; Figure
). There is also evidence that geographic isolation plays a significant role
in yucca diversification (Althoff et al., 2012; Smith et al., 2008). These together suggest that while coevolution plays a role in the
emergence of these mutualisms, it is not the exclusive mechanism and may not even be the primary one.
: Cophylogenetic comparison of the pollinators associated with the 15 fig species studied. Ficus and pollinator
phylogenies used were indicated with symbol of figs and wasp separately. Tip-name colors indicate subgeneric classification.
Extensive phylogenetic incongruence is shown for each pair of phylogenies (credit: modified from Wang et al. 2021).
References Althoff, D.M., Segraves, K.A., Smith, C.I., Leebens-Mack, J., & Pellmyr, O. (2012). Geographic isolation trumps coevolution as a driver of yucca and yucca moth diversification. Molecular Phylogenetics and Evolution, 62, pp. 898-906. de Mazancourt, C., Loreau, M., & Dieckmann, U. (2001). Can the evolution of plant defense lead to plant-herbivore mutualism? Am. Nat., 158, pp. 09-123. de Mazancourt, C., Loreau, M., & Dieckmann, U. (2005). Understanding mutualism when there is adaptation to the partner. J. Ecol., 93, pp. 305-314. Hembry, D.H., Yoder, J.B., & Goodman, K.R. (2014). Coevolution and the diversification of Llfe. The American Naturalist, 184(4), pp. 425-38. https://doi.org/10.1086/677928. Kiers, T.E., Palmer, T.M., Ives, A.R., Bruno, J.F. & Bronstein, J.L. (2010). Mutualisms in a changing world: An evolutionary perspective. Ecol. Lett., 13, pp. 1459-1474. Moe, A.M., & Weiblen., G.D. (2012). Pollinator-mediated reproductive isolation among dioecious fig species (Ficus, Moraceae). Evolution, 66, pp. 3710-3721. Pellmyr, O. (2003). Yuccas, yucca moths, and coevolution: A review. Ann. Mo. Bot. Gard., 90, pp. 35-55.
Sachs, J. & Simms, E. (2006). Pathways to mutualism breakdown. Trends Ecol. Evol., 21, pp. 585-592. Sachs, J., Skophammer, R., Bansal, N. & Stajich, J. (2014). Evolutionary origins and diversification of proteobacterial mutualists. Proc. R. Soc. B Biol. Sci., 281, 20132146. Smith, C.I., Pellmyr, O., Althoff, D.M., Balcázar-Lara, M., Leebens-Mack, K., & Segraves, K.A. (2008). Pattern and timing of diversification in Yucca (Agavaceae): Specialized pollination does not elevate rates of diversification. Proceedings of the Royal Society B: Biological Sciences, 275, pp. 249-258. van der Niet, T., & Johnson, S.D. (2012). Phylogenetic evidence for pollinator-driven diversification of angiosperms. Trends in Ecology and Evolution, 27, pp. 353-361. Weeks, A., Turelli, M., Harcombe, W., Reynolds, K. & Hoffmann, A. (2007). From parasite to mutualist: Rapid evolution of Wolbachia in natural populations of Drosophila. PLoS Biol., 5, e114. Yamamura, N. (1993). Vertical transmission and evolution of mutualism from parasitism. Theor. Popul. Biol., 44, pp. 95-109. Yamamura, N. (1996). Evolution of mutualistic symbiosis: A differential equation model. Res. Popul. Ecol., 38, pp. 211-218. Contributors and Attributions This chapter was written by Aaron Howard with text taken from the following CC-BY resources: Johnson, C.A., Smith, G.P., Yule, K. et al. (2021). Coevolutionary transitions from antagonism to mutualism explained by the Co-Opted Antagonist Hypothesis. Nat Commun, 12, 2867. https://doi.org/10.1038/s41467-021-23177-x Segraves, K.A. (2010). Branching out with coevolutionary trees. Evo. Edu. Outreach, 3, pp. 62-70. https://doi.org/10.1007/s12052-009-0199-z Wang, G., Zhang, X., Herre, E.A. et al. (2021). Genomic evidence of prevalent hybridization throughout the evolutionary history of the fig-wasp pollination mutualism. Nat Commun., 12, 718. https://doi.org/10.1038/s41467-021-20957-3 Weeks, A., Turelli, M., Harcombe, W., Reynolds, K. & Hoffmann, A. (2007). From parasite to mutualist: Rapid evolution of Wolbachia in natural populations of Drosophila. PLoS Biol., 5, e114. 17.3: Evolution of Mutualisms is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
Maintenance of mutualism The stability of mutualisms can be undermined by cheating. Cheating is a behavior whereby organisms receive a benefit at the cost of other organisms. Cheating is common in many mutualistic and altruistic relationships (Ferriere et al., 2002). A cheater is an individual who does not cooperate (or cooperates less than their fair share) but can potentially gain the benefit from others cooperating (West et al., 2006). Cheaters are also those who selfishly use common resources to maximize their individual fitness at the expense of a group (McLean & Gudelj, 2006). Simple two-player game theory and the associated evolutionary theory indicate that cheating can be evolutionarily stable, but there are mechanisms to regulate it (Foster & Kokko, 2006). The mutualism between legume plants and rhizobia (nitrogen-fixing soil bacteria) is an example where this regulation occurs. Rhizobia establish symbiotic organs termed root nodules on the roots of their host, and proliferate by extracting nutrients from the host plant. In turn, they supply their host plants with nitrogen resources produced by nitrogen gas fixation. This mutual nutrient exchange should promote the fitness of both organisms and thereby strengthen the symbiotic relationship. This beneficial effect, known as "partner fidelity feedback", is assumed as a stabilizing factor for the mutualistic relationship (Sachs et al., 2004; Weyl et al., 2010; Friesen & Jones, 2012; Friesen, 2012). On the other hand, naturally occurring rhizobium strains vary in their nitrogen fixation activity, and ineffective rhizobia that colonize their host plants without undertaking nitrogen fixation in their root nodules are ubiquitous (Gibson et al., 1975; Bottomly & Jenkins, 1983; Moawad, 1998; Burdon et al., 1999). Because the nitrogen fixation reaction consumes much energy (or costs), such parasitic cheaters could use surplus energy for their own growth or for synthesizing storage substances. Consequently, they are likely to proliferate more efficiently than nitrogen-fixing cooperators, posing a risk to the symbiotic interaction. Rhizobia are therefore exposed to two opposite effects that simultaneously promote (by providing benefit) and destabilize (by incurring cost) the mutualistic relationship.
An uproot plant shows long thin roots with small nodules made of root tissue.
: Nitrogen-fixing nodules in legumes. Image by Terraprima is licensed under CC BY-SA 3.0.
Despite the widespread presence of ineffective rhizobia, the legume-rhizobia symbiosis is evolutionarily stable. Host sanctioning is a potential mechanism that stabilizes the symbiotic interaction, where plants punish more parasitic cheaters by reducing nutrient supply based on their symbiotic performance (Friesen & Jones, 2012; Friesen, 2012; Kiers & Denison, 1998).
Another example is found within the yucca-yucca moth mutualisms. "Cheating" sometimes happens when the yucca moth deposits too many eggs in one plant. In this case, the yucca plant has little to no benefits from this interaction. However, the plant has a unique way of sanctioning this behavior. While the sanctions against cheating often occurs directly to the individual, in this case, the constraint occurs to the individual's offspring. The yucca plant can "abort" the moths by aborting the flowers. Pellmyr and Huth (1994) found that there is selective maturation for flowers that have low egg loads and high number of scars (and therefore a high amount of pollen). In this way, there is selection against the "cheaters" who try to use the yucca plant without providing the benefits of pollination.
: Two yucca moth females in a yucca flower. The female on the right is laying an egg and clearly shows the pollen
ball on the underside of her head. The female on the left is actively pollinating with her maxillary tentacles. Photograph by Olle
Yucca plants will drop flowers if their obligate pollinators, the yucca moths, lay too many eggs. This reduces fitness for both the plant and the moth that laid the egg, and is a form of sanctioning by the plant. However, devoting resources to growing a fruit with too many yucca moth larvae on it would reduce the plant's fitness even more than aborting the flower does. If the flower is aborted, the cost to fitness for the pollinator is very high, making this an effective sanction against moths that try to "cheat" the plant by laying too many eggs.
Neither option is great for the plant - but at what point is it worse for the plant's fitness to retain and invest resources in a flower with too many eggs, rather than dropping the flower and sacrificing any possible surviving seeds? It turns out that most yucca fruits that are retained by the plant contain about 130 seeds, but about 20% of those seeds (26 seeds) are eaten by larvae (Alexander et al.). Therefore, plants begin to drop flowers when the number of larvae present are likely to consume more than 20% of the seeds! In the graph below, you can see the probability of retaining versus dropping a flower based on the number of larvae present. This graph was simulated from the real values found by Pellmyr and Huth in their groundbreaking 1994 paper, which showed that mutualisms are not always strictly collaborative, but can involve tension between opposing forces (the plant needs pollination, but doesn't 'want' seeds eaten, the moth needs to lay as many eggs as it can) held in check by natural selection.
: This graph shows the probability of retaining a flower (0) versus aborting a flower (1) based on the number of
eggs laid on that flower. As the number of eggs increases, the plant becomes more likely to abort the flower, beginning to
switch when there are ~6.5 larvae, meaning that most larvae eat ~4 seeds. However, as you can see from the green (retained)
and tan (dropped) histograms, not every plant responds in the same way. Some plants retain flowers even with over 15 eggs
laid, while others will drop flowers with only 2 eggs.
1. How many larvae could a flower tolerate if each flower had 250 seeds, instead of 130?
2. How many larvae could a flower tolerate if each larva had to eat 10 seeds, instead of 4?
References Alexander, R.R., Pond, F.W., & Rodgers, J.E. (n.d.). Yucca (L.). Forest Handbooks. https://www.fs.fed.us/rm/pubs_other/wo_AgricHandbook727/wo_AgricHandbook727_1175_1177.pdf
Bottomley. P, & Jenkins, M. (1983). Some characteristic of Rhizobium meliloti isolates from alfalfa fields in Oregon. Soil Sci. Soc. Am., J 47, pp. 1153-1157.
Burdon, J., Gibson, A., Searle, S., Woods, M., & Brockwell, J. (1999). Variation in the effectiveness of symbiotic associations between native rhizobia and temperate Australian Acacia: Within-species interactions. J. Appl. Ecol., 36, pp. 398-408.
Ferriere, R., Bronstein, J.L., Rinaldi, S., Law, R., & Gauduchon, M. (2002). Cheating and the evolutionary stability of mutualisms. Proc. R. Soc. Lond., 269(1493), pp. 773-780. doi:10.1098/rspb.2001.1900. PMC 1690960. PMID 11958708.
Foster, K.R., & Kokko, H. (2006). Cheating can stabilize cooperation in mutualisms. Proceedings of the Royal Society B: Biological Sciences, 273(1598), pp. 2233-2239. doi:10.1098/rspb.2006.3571. PMC 1635526. PMID 16901844.
Friesen, M.L., & Jones, E.I. (2012). Modelling the evolution of mutualistic symbioses. Methods Mol. Biol., 804, pp. 481-499.
Friesen, M.L. (2012). Widespread fitness alignment in the legume-rhizobium symbiosis. New Phytol., 194, pp. 1096-1111. Gibson, A., Curnow, B., Bergersen, F., Brockwell, J., & Robinson, A. (1975). Studies of field populations of Rhizobium: Effectiveness of strains of Rhizobium trifolii associated with Trifolium subterraneum L. pastures in South-Eastern Australia. Soil Biol. Biochem., 7, pp. 95-102. Kiers, E., & Denison, R. (2008). Sanctions, cooperation, and the stability of plant Rhizosphere mutualisms. Annu. Rev. Ecol. Evol. Syst., 39, pp. 215-236. MacLean, R.C., & Gudelj, I. (2006). Resource competition and social conflict in experimental populations of yeast. Nature, 441(7092), 498-501. Bibcode:2006Natur.441..498M. doi:10.1038/nature04624. PMID 16724064. S2CID 4419943. Moawad, H., El-Din, S., & Abdel-Aziz, R. (1998). Improvement of biological nitrogen fixation in Egyptian winter legumes through better management of Rhizobium. Plant Soil, 204, pp. 95-106. Pellmyr, O., & Huth, C.J. (1994). Evolutionary stability of mutualism between yuccas and yucca moths. Nature, 372(6503), pp. 257-260. Bibcode:1994Natur.372..257P. doi:10.1038/372257a0. S2CID 4330563. Sachs, J., Mueller, U., Wilcox, T., & Bull, J. (2004). The evolution of cooperation. Quart. Rev. Biol., 79, pp. 135-160. West, S.A., Griffin, A.S., Gardner, A., & Diggle, S.P. (2006). Social evolution theory for microorganisms. Nature Reviews Microbiology, 4(8), pp. 597-607. doi:10.1038/nrmicro1461. PMID 16845430. S2CID 18451640. Weyl, E.G., Frederickson, M.E., Yu, D.W., & Pierce, N.E. (2010). Economic contract theory tests models of mutualism. Proc. Natl. Acad. Sci. USA., 107, pp. 15712-15716. Contributors and Attributions This chapter was written by Aaron Howard with text taken from the following CC-BY resources. Exercise text, data simulation, and code written by Castilleja Olmsted: Cheating (biology) by Wikipedia, the free encyclopedia Fujita H, Aoki S, Kawaguchi M (2014) Evolutionary Dynamics of Nitrogen Fixation in the Legume-Rhizobia Symbiosis. PLoS ONE 9(4): e93670. doi:10.1371/journal.pone.0093670 17.4: Maintenance of Mutualisms is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.
17.5: Types of Commensalisms Phoresis Phoresis or phoresy is a non-permanent, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to another (the host) solely for the purpose of travel (White et al., 2017). Phoresis has been observed directly in ticks and mites since the 18th century (Houck & O'Connor, 1991), and indirectly in fossils 320 million years old (White et al., 2017). It is not restricted to arthropods or animals; plants with seeds that disperse by attaching themselves to animals are also considered to be phoretic (Houck, 2009).
: Male Bombus hypnorum with phoretic mites. Photograph by Dimitr Boevski.
The strict definition of phoresis excludes cases in which the relationship is permanent (e.g. that of a barnacle surviving on a whale) or those in which the phoront gains any kind of advantage from the host organism (e.g. remoras attaching to sharks for transportation and food) (Houck & O'Connor, 1991). Phoresis is a commensal relationship and deviations result in mutualistic or parasitic relationships. Phoretic relationships can become parasitic if a cost is inflicted upon the host, such as if the number of mites on a host begins impeding its movement. Parasitic relationships could also evolve for from phoretic ones if the phoront gains a fitness advantage from the death of a host (e.g. nutrition). Mutualistic relationships could also evolve if the phoront began to confer a benefit to the host (e.g. predator defense) (White et al., 2017). The evolutionary plasticity of phoretic relationships allow them to potentially add to the complexity and diversity of ecosystems (Houck, 2009).
Cases in which the phoront parasitizes or preys upon the host organism after travel are still considered phoresis, as long as the travel behavior and the feeding or parasitizing behavior are separate (White et al., 2017). Similarly, some pseudoscorpions prey
upon the same species that act as their phoretic host. The behaviors are completely separate, however, since the pseudoscorpion uses anatomical features specifically for predation when treating the host as prey, but employs anatomical features used for phoresis when travelling (Poinar et al., 1998).
Inquilinism An inquiline is an animal that lives commensally in the nest, burrow, or dwelling place of an animal of another species. For example, some organisms such as insects may live in the homes of gophers or the garages of human beings and feed on debris, fungi, and roots. The most widely distributed types of inquiline are those found in association with the nests of social insects, especially ants and termites - a single colony may support dozens of different inquiline species. The distinctions between parasites, social parasites, and inquilines are subtle, and many species may fulfill the criteria for more than one of these, as inquilines do exhibit many of the same characteristics as parasites. However, parasites are specifically not inquilines, because by definition they have a deleterious effect on the host species (Nash & Boomsma, 2008), while inquilines have not been confirmed to do so. In the specific case of termites, the term "inquiline" is restricted to termite species that inhabit other termite species' nests (Florencio et al., 2013; Cunha et al., 2003; Hugo et al., 2019), whereas other arthropods cohabiting termitaria are called "termitophiles" (Rosa et al., 2018; Oliveira, 2018). It is important to reiterate that inquilinism in termites (Blattodea, formerly Isoptera) contrasts with the inquilinism observed in other eusocial insects such as ants and bees (Hymenoptera), even though the term "inquiline" has been adopted in both cases. A major distinction is that, while in the former the species mostly resemble forms of commensalism, the latter includes species currently confirmed as social parasites, thus, being closely related to parasitism. Inquilines are known especially among the gall wasps (Cynipidae family). In the sub-family Synerginae, this mode of life predominates. These insects are similar in structure to the true gall-inducing wasp but do not produce galls, instead, they deposit their eggs within those of other species. They infest certain species of galls, such as those of the blackberry and some oak galls, in large numbers, and sometimes more than one kind occur in a single gall. Perhaps the most remarkable feature of these inquilines is their frequent close resemblance to the insect that produces the gall they infest (Rines, 2020; Discover Life, 2011). The term inquiline has also been applied to aquatic invertebrates that spend all or part of their life cycles in phytotelmata, waterfilled structures produced by plants (Cronk & Fennessy, 2001). For example, Wyeomyia smithii, Metriocnemus knabi, and Habrotrocha rosa are three invertebrates that make up part of the microecosystem within the pitchers of Sarracenia purpurea (Cochran-Stafira & von Ende, 1998). Some species of pitcher plants like the Nepenthes and Cephalotus produce acidic, toxic or digestive fluids and host a limited diversity of inquilines. Other pitcher plant species like the Sarracenia or Heliamphora host diverse organisms and depend to a large extent on their symbionts for prey utilization (Adkassnig et al., 2011).
A photo from a microscope of a long microorganism with hairlike structures. : Wyeomyia smithii larva is an inquiline species in the pitcher leaves of Sarracenia purpurea. "Wyeomyia smithii" by Rkitko is licensed under CC BY-SA 3.0.
Metabiosis Metabiosis is a more indirect dependency, in which one organism creates or prepares a suitable environment for a second. Examples include maggots, which develop on and infest corpses, and hermit crabs, which use gastropod shells to protect their bodies.
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Discover Life: Family Cynipidae: Subfamily Synerginae visited 1 January 2011
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Contributors and Attributions This chapter was written by Aaron Howard with text taken from the following CC-BY resources: Commensalism by Wikipedia, the free encyclopedia Phoresis by Wikipedia, the free encyclopedia Inquiline by Wikipedia, the free encyclopedia 17.5: Types of Commensalisms is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by LibreTexts.