Some of the species drawn into mutualistic interactions become co-mutualists, contributing as well as benefiting from the relationship, whereas others become cheaters that only exploit the relationship.
Many of the bacteria in question are genuinely mutualistic with their hosts, helping the process of digestion or warding off pathogenic bugs.This is scarcely explored territory.
Certain species, for example, grow in a mutualistic relationship with fungi, forming composite organisms known as lichens.
In this mutualistic association, the photosynthetic microbes synthesize nutrients for the fungus, and in return the fungus provides protective cover for the algae or cyanobacteria.
In antagonistic relationships the interaction is detrimental to individuals of either one or both species; in commensal relationships (commensalism) one species benefits while the other remains unaffected; and in mutualistic relationships (mutualism) both species benefit.
The second kind comprises the mutualistic (symbiotic) bacteria; examples include Rhizobium, associated with leguminous plants (e.g., various members of the pea family); Frankia, associated with certain dicotyledonous species (actinorhizal plants); and certain Azospirillum species, associated with cereal grasses.
These benefits may vary from one population to another, thereby causing mutualistic relationships that exist between the same species to evolve in different directions in different populations.
Some species surrounding these vents feed on these bacteria, but other species have formed long-term, reciprocally beneficial relationships (mutualistic symbioses) with sulfur bacteria.
Species that enter into symbiotic, or mutualistic, interactions may be brought together by advertising coloration.
Mycorrhizal fungi establish a mild form of parasitism that is mutualistic, meaning both the plant and the fungus benefit from the association.
