Essay on reproductive isolating mechanisms (1500 words)

Essay by thepiemanUniversity, Bachelor's September 2004

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Reproductive Isolating Mechanisms

In the 1940s, Ernst Mayr coined the term Biological Species Concept that was subsequently widely embraced by the scientific community. The definition stated that "Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups". Certain mechanisms are in place to prevent species from interbreeding with others and these are referred to as reproductive isolating mechanisms, which are biological incompatibilities. There are many mechanisms acting on natural populations and these are broadly grouped into two categories namely prezygotic and postzygotic mechanisms.

Prezygotic isolating mechanisms are those mechanisms that isolate species before fertilisation i.e. before a zygote is formed. They include geographical, ecological, temporal, ethological, mechanical, morphological and gametic isolation. These mechanisms lesson the possibility of gametes from different species coming into contact and hence forming a zygote.

One prezygotic isolating mechanism is ecological isolation, also referred to as habitat isolation.

Ecological isolation prevents different species that live in the same territory but different habitats from interbreeding. These species are referred to as sympatric species since they occur in the same territories. Individuals mate in their preferred habitat, and therefore do not meet individuals of other species with different ecological preferences. An example of ecological isolation occurs within the Rana genus. R. grylio, the pig frog and R. areolata, the gopher frog both occur around New Orleans, Louisiana. The exceptionally aquatic pig frog lives in deep ponds, lakes and marshes amongst surfacing vegetation and breeds in deep water so has no contact with the gopher frog which lives in burrows during the day, and in the swamp margins at night and breeds in shallow water. This way the possibility of interbreeding between the two species is eliminated.

Temporal isolation, also known as seasonal isolation is a prezygotic mechanism that prevents interbreeding...