Differentiation in the elephants

The historical tendency of proboscidean taxonomists to be splitters to an extreme degree in naming genera and species also extended to subspecies. Henry Fairfield Osborn listed 18 subspecies for Loxodonta africana in his 1942 tome. For Elephas maximus, P.E.P. Deraniyagala alone named eight or nine subspe cies, including several for Sri Lanka. With the available morphological data, these were whittled down to two subspecies for Loxodonta africana (but see section 1.9.4) and three for Elephas maximus. The development of new techniques in molecular biology now offers the possibility of offering greater clarity to the issue of speciation or subspeciation in terms of the underlying genetics. With the recent evidence for recognizing two or more distinct species of elephants in Africa, the splitters may still have the last laugh.

Molecular techniques also have the potential of teasing out the complexities of population structure and differentiation across a range of spatial scales, from local herd to regional and continentwide scales. Several laboratories around the world are currently addressing questions relating to the molecular genetics of the elephants. Unlike for many other mammal species, only limited results are presently available for elephants. These should thus be interpreted with caution. Some of the early studies, especially those related to genetic diversity in elephant populations, were based on variation in proteins or enzymes (allo-zymes) that are the products of genes. These have been quickly overtaken by the more direct examination of DNA, the repository of genetic information. I thereby confine this account only to the DNA studies.

The DNA studies can be broadly categorized into those that profile DNA found in mitochondria, the tiny cell organelles or "powerhouses" inherited only maternally, and those that profile the DNA in the cell nucleus and combine both maternal and paternal inheritance. For technical reasons, the elucidation of much smaller quantities of mitochondrial DNA (mtDNA) in a cell has been easier; incidentally, the mtDNA changes through mutation about 10 times as fast as nuclear DNA in evolutionary time and is thus particularly suitable for studies of phylogeny. Most of the early DNA studies of elephants focused on mtDNA. Only very recently have techniques to profile nuclear DNA in certain variable segments been developed and applied to elephants. It is obviously important to profile the nuclear DNA because this constitutes the bulk of the genetic information of an individual and has both maternal and paternal contributions.

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