Ectosymbiosis

Ectosymbiosis is a form of symbiotic behavior in which an organism lives on the body surface of another organism (the host), including internal surfaces such as the lining of the digestive tube and the ducts of glands. The ectosymbiotic species, or ectosymbiont, is generally an immobile (or sessile) organism existing off of biotic substrate through mutualism, commensalism, or parasitism. Ectosymbiosis is found throughout a diverse array of environments and in many different species. In some species the symbiotic environment provided by both the parasite and host are mutually beneficial. In recent research it has been found that these micro-flora will evolve and diversify rapidly in response to a change in the external environment, in order to stabilize and maintain a beneficial ectosymbiotic environment. Ectosymbiosis has evolved independently many times to fill a wide variety of ecological niches, both temperate and extreme. Such temperate regions include the seas off the coast of Singapore while the extreme regions reach to the depths of Antarctica and hydrothermal vents. It likely evolved as a niche specialization, which allowed for greater diversity in ectosymbiotic behavior among species. Additionally, in the case of mutualism, the evolution improved the fitness of both species involved, propagating the success of ectosymbiosis. Ectosymbiosis has independently evolved through convergent evolution in all domains of life. Ectosymbiosis allows niches to form that would otherwise be unable to exist without the support of their host. Inherently this added niche opens up a new branch off of the evolutionary tree The evolutionary success of ectosymbiosis is based on the benefits experienced by the parasite and the host. Due to the dependence of the parasite on the host and the associated benefits and cost to both the parasite and host, the two will continue to coevolve as explained by the Red Queen hypothesis. The Red Queen hypothesis states that a host will continually evolve defenses against a parasitic attack, and the parasite species will also adapt to these changes in the host defense.