Commensalism Interaction- Definition, Types and Examples

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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
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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.
  • 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.
  • 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).
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About Author

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Anupama Sapkota

Anupama Sapkota has a bachelor’s degree (B.Sc.) in Microbiology from St. Xavier's College, Kathmandu, Nepal. She is particularly interested in studies regarding antibiotic resistance with a focus on drug discovery.

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