Mutualism

Mutualism is a biological interaction that is beneficial to both parties. Most mutualisms are facultative, meaning the partners can successfully live apart. However, some mutualisms are so intimate that the interacting species can no longer live without each other; they have a mutually obligate interdependence. Many mutualisms are fascinating in their intricacies and reciprocal usefulness as is apparent in the examples described below.

Many species of angiosperm plants require the services of an animal vector to achieve pollination. The animal benefits in this mutualism from access to a source of food of nectar or pollen, while the plant benefits through having its gametes fertilized. Some pollination systems involve a remarkably tight co-evolution of the plant and animal species, with morphological and behavioral adaptations that make the mutualistic interaction more efficient and more interdependent. Some species of orchids, for example the genus Ophrys, have a floral structure and coloration that closely mimics that of the female of their pollinating species of wasp so that the plant becomes pollinated when the male wasp is tricked and attempts pseudo-copulations with its flowers. There are numerous other examples of similarly extraordinary co-adaptations of plant-animal pollination systems.

Another plant-insect mutualism involves a tropical ant (Pseudomyrmex ferruginea ) and a shrub known as the bull’s horn acacia (Acacia cornigera ). This acacia has evolved hollow thorns that are used by the ants as protected nesting sites. In addition, the ants feed on proteinrich exudates at the tips of the leaflets of the acacia. In return, the ants protect the acacia from competition with other plants by weeding the vicinity of their host of encroaching foliage. The ants also protect the acacia from many defoliators by killing herbivorous insects and attacking larger herbivores such as grazing mammals. Many other species of ants have developed mutualistic interactions with plant species. This fact is evidenced by the independent evolution of extrafloral nectaries by various families of plants. These organs exude nectar from leaves, stems, or branches, attracting ants that help to protect the plants from competition and herbivory.

A marine mutualism involves unicellular algae known as zooxanthellae and corals, a type of coelenterate animal. In this mutualism the coral provides the algae with shelter and inorganic nutrients, while the pigmented algae provide photosynthate. Sometimes this mutualism is upset by environmental stresses associated with unusually warm or cool water temperatures, a change in salinity, or excessive exposure to sunlight or shading. This leads to expulsion of the zooxanthellae by the coral, a phenomenon known as “bleaching,” which may lead to death of the coral unless it can re-establish another algal mutualism.

Another interesting mutualism involves two animals, an African bird known as the honey guide (Indicator indicator ) and a mammal known as the honey badger (Melliovora capensis ). In this relationship the honey guide finds bee hives and then actively leads the honey badger to its discovery. The badger tears the hive apart with its strong claws and then feeds on the honey, while the bird feeds on the bee larvae and pupae.

See also Symbiosis.

Bill Freedman

Mutualism

Mutualism is a biological interaction that is beneficial to both parties. Most mutualisms are facultative, meaning the partners can successfully live apart. However, some mutualisms are so intimate that the interacting species can no longer live without each other; they have a mutually obligate interdependence. Many mutualisms are fascinating in their intricacies and reciprocal usefulness as is apparent in the examples described below.

Many species of angiosperm plants require the services of an animal vector to achieve pollination . The animal benefits in this mutualism from access to a source of food of nectar or pollen, while the plant benefits through having its gametes fertilized. Some pollination systems involve a remarkably tight co-evolution of the plant and animal species, with morphological and behavioral adaptations that make the mutualistic interaction more efficient and more interdependent. Some species of orchids, for example the genus Ophrys, have a floral structure and coloration that closely mimics that of the female of their pollinating species of wasp so that the plant becomes pollinated when the male wasp is tricked and attempts pseudo-copulations with its flowers. There are numerous other examples of similarly extraordinary co-adaptations of plant-animal pollination systems.

Another plant-insect mutualism involves a tropical ant (Pseudomyrmex ferruginea) and a shrub known as the bull's horn acacia (Acacia cornigera). This acacia has evolved hollow thorns that are used by the ants as protected nesting sites. In addition, the ants feed on protein-rich exudates at the tips of the leaflets of the acacia. In return, the ants protect the acacia from competition with other plants by weeding the vicinity of their host of encroaching foliage. The ants also protect the acacia from many defoliators by killing herbivorous insects and attacking larger herbivores such as grazing mammals . Many other species of ants have developed mutualistic interactions with plant species. This fact is evidenced by the independent evolution of extrafloral nectaries by various families of plants. These organs exude nectar from leaves, stems, or branches, attracting ants that help to protect the plants from competition and herbivory.

A marine mutualism involves unicellular algae known as zooxanthellae and corals, a type of coelenterate animal. In this mutualism the coral provides the algae with shelter and inorganic nutrients , while the pigmented algae provide photosynthate. Sometimes this mutualism is upset by environmental stresses associated with unusually warm or cool water temperatures, a change in salinity, or excessive exposure to sunlight or shading. This leads to expulsion of the zooxanthellae by the coral, a phenomenon known as "bleaching," which may lead to death of the coral unless it can re-establish another algal mutualism.

Another interesting mutualism involves two animals, an African bird known as the honey guide (Indicatorindicator) and a mammal known as the honey badger (Melliovora capensis). In this relationship the honey guide finds bee hives and then actively leads the honey badger to its discovery. The badger tears the hive apart with its strong claws and then feeds on the honey, while the bird feeds on the bee larvae and pupae.

See also Symbiosis.

Bill Freedman

mu·tu·al·ism / ˈmyoōchoōəˌlizəm/ • n. the doctrine that mutual dependence is necessary to social well-being. ∎  Biol. symbiosis that is beneficial to both organisms involved.DERIVATIVES: mu·tu·al·ist n. & adj.mu·tu·al·is·tic / ˌmyoōchoōəˈlistik/ adj.mu·tu·al·is·ti·cal·ly / ˌmyoōchoōəˈlistik(ə)lē/ adv.

Mutualism

A mutualism is a symbiosis where two or more species gain mutual benefit from their interactions, and suffer negative impacts when the mutualistic interactions are prevented from occurring. Mutualism is a form of symbiosis where the interactions are frequently obligatory, with neither species being capable of surviving without the other. A well-known example of mutualism is the relationship between certain species of algae or blue-green bacteria and fungi that results in organisms called lichens . The fungal member of the relationship provides a spatial habitat for the algae, which in turn provide energy from photosynthesis to the fungus. Mutualistic interactions are thought to be the origin of the many cell organelles like mitochondria and chloroplasts, which may have resulted from the acquisition of free-living phytoplankton and other single-celled organisms by host species. Both the incorporated cell and the host soon evolved so that neither could exist without the other.

[Marie H. Bundy ]

mutualism An interaction between two species in which both species benefit. (The term symbiosis is often used synonymously with mutualism.) A well-known example of mutualism is the association between termites and the specialized protozoans that inhabit their guts. The protozoans, unlike the termites, are able to digest the cellulose of the wood that the termites eat and release sugars that the termites absorb. The termites benefit by being able to use wood as a foodstuff, while the protozoans are supplied with food and a suitable environment. See also mycorrhiza.