Biodiversity and intraspecific genetic variation

Biodiversity is mostly discussed at the level of species, but genetic variation within species may be as important as variation between species. It enables organisms to adapt to environmental changes. The requirement for genetic variation differs however widely between species and groups of species. Animal species at the top of the food web, such as large carnivorous mammals, tend to have a remarkably small genetic variation, presumably due to a constant ecological niche. Many other organisms must be genetically ‘prepared’ to meet environmental changes. As an example, for organisms relying on camouflage a colour polymorphism matching altered environments in space and time is of selective importance. Several mechanisms are involved in maintaining a genetic variation. One such mechanism is balanced polymorphism based on a higher viability of heterozygotes as compared to both homozygotes. A major part of DNA in multicellular organisms does not have any discernible function, but behave as parasites. Important elements in that respect are mobile DNA elements, ‘jumping genes’, which can move from one place in the genome to another, causing mutations at site of insertion and increased genetic variation. Some mobile elements have been shown to move from one individual and species to another asexually. The mechanism behind this ‘horizontal transfer’ is unknown, but presumably is mediated by microorganisms. Protective devices against these parasitic DNA elements have been developed by many organisms.