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Commensalism Definition
Commensalism is a type of ecological interaction between two or more species where one of the species is benefitted without either harming or benefitting the other.
- Commensalism is a positive interaction but is quite different interactions like mutualism or parasitism.
- It is usually a long term relationship where some species remain in the interaction for their entire life.
- The interaction mostly exists between a larger host and a smaller commensal. The organisms that provide the benefit but are unaffected is the host and the organism which is benefitted from the interaction is the commensal.
- The commensal might even demonstrate different forms of structural and functional adaptation based on the relationship.
- The term commensalism is derived from the term ‘commensal’ which means eating at the same table. The term was popularized in ecology by Pierre-Joseph van Beneden in 1876.
- The benefits obtained by the commensal from the interaction can either be services like transportation, protection, or resources like nutrients.
- Commensalism, like most ecological interaction, has played essential roles in evolution as the interactions and adaptations accumulate over time.
- This form of interaction can exist between the organisms of the same species or different species.
![Commensalism Interaction](https://microbenotes.com/wp-content/uploads/2021/02/Commensalism-Interaction-1.jpeg)
Types of Commensalism
Commensalism is of different types depending on the strength and duration of the interaction and the purposes.
1. Inquilinism
- Inquilinism is a type of commensalism where one of the species uses the body or a cavity with the body of the other organisms as a living.
- In this form of commensalism, one of the species is benefitted as it attains shelter while the other species remain unaffected.
- Inquilinism exhibits resource commensalism where the commensal attains a resource in the form of shelter.
Example- Scarab beetles and flies
- Scarab beetles roll balls of dung which they then bury underground in burrows as a food source for their immatures. When they roll the ball, small flies are attracted to the dung.
- The adult flies lay their eggs in the ball and escape from the burrow before the beetles seal the holes.
- The fly larvae in the ball share the dung with the beetles’ larvae without negatively impacting the host.
- The larvae beetles then develop into adult beetles and dig out of the burrow while releasing the adult flies.
- Thus, the species exist in a commensal relationship for a short period of time, and the interaction is essential for the lifecycle of the flies.
2. Metabiosis
- Metabiosis is a form of commensalism where the host species unintentionally creates a suitable environment for the commensal.
- In metabiosis, most commensal use the remains of some part of the remains of the host for their benefit.
- The commensal might use the remains of the host as tools for their survival or as a form of protection.
- The host species involved in this form of interaction are usually large, whereas the commensals are small.
Example- Hermit crabs and gastropod shell
- Hermit crabs live inside the empty gastropod shell to protect their soft abdominal exoskeleton.
- The shell protects the animals against predation, desiccation, thermal and osmotic stress. Hermits continuously evolve to rapidly access good quality shells through competitive interactions with other individuals and aggregation.
- Some of the hermit crabs also carry the shells around with them as portable homes which also protect the organisms against predation and other conditions.
- The ability of hermit crabs to utilize gastropod shells as a form of living space is due to the availability of different shapes and sizes of shells.
3. Phoresy
- Phoresy is a form of interaction between two species where the commensal or phoront latches onto the host animals for dispersal without inducing parasitism.
- The term phoresy is derived from the Greek word ‘phorein’ meaning ‘to carry’.
- In a typical interaction, the phoront or phoretic organisms is an animal usually a nematode or mite, with the ability to travel limit distances and thus, requires aid in dispersal with the help of a mobile host.
- The benefit obtained by the phoront is measured in terms of dispersal instead of nutritional benefits, like in the case of parasitism.
- Phoresy is a temporary interaction that continues only until the phoront reaches the desired distance. The interaction can, however, turn parasitic over time.
- Phoretic interactions exist between species of the entire animal kingdom and thus are extremely diverse.
Example- Caenorhabditis remanei (soil nematode) and molluscs
- Caenorhabditis remanei is a soil nematode that has a limited dispersal ability on its own due to the small size and sensitivity to desiccation.
- The species thus depends on other animals like slugs, snails, and isopods for dispersal to longer distances.
- The interactions are strictly used for dispersal and to avoid harsh environmental conditions.
- Most of the species remain on the body of the slugs, but in some cases, the organisms can be found within the intestine of the slugs.
4. Microbiota
- Microbiota is a group of microorganisms that exist in a commensal interaction with the host surface as they colonize a particular tissue surface.
- The system formed is termed normal microbiota, and it mostly comprises bacteria with few fungi, protozoans, and viruses.
- These species exist in a commensal relationship with the host species and depend on the host for nutrition and living space.
- Even though the population of a microbiota develops in close parallel with the host, they do not cause harm to the host body.
- However, in some cases, in individuals with reduced immunity and immune-compromised conditions, these species might cause different diseases.
Example- Gut microbiota in human
- In humans, a large group of microorganisms resides in different parts of the body, but the most diverse and the largest population of such organisms reside in the gut.
- These microbes exist on the surface of human tissue and depend on the host for nutrients and living space.
- Even though the microorganisms take up nutrients from the digestive system, it doesn’t cause any harm to the host unless the species is pathogenic.
- In some cases, the species might be opportunistic pathogens and cause diseases in immunocompromised individuals.
References and Sources
- (2008) Commensalism. In: Capinera J.L. (eds) Encyclopedia of Entomology. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-6359-6_775
- White, P Signe et al. “Phoresy.” Current biology: CB vol. 27,12 (2017): R578-R580. doi:10.1016/j.cub.2017.03.073
- Sourakov A. (2008) Inquilines and Cleptoparasites. In: Capinera J.L. (eds) Encyclopedia of Entomology. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-6359-6_1536
- Petersen, C., Hermann, R.J., Barg, MC. et al. Travelling at a slug’s pace: possible invertebrate vectors of Caenorhabditis nematodes. BMC Ecol 15, 19 (2015). https://doi.org/10.1186/s12898-015-0050-z
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- <1% – https://en.wiktionary.org/wiki/metabiosis
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- <1% – https://en.wikipedia.org/wiki/Dung_beetle