Parental Contributions in Elephants

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Science  21 Jan 2005:
Vol. 307, Issue 5708, pp. 319
DOI: 10.1126/science.307.5708.319a

African forest elephants and their much larger savanna cousins are now recognized as two distinct species that underwent an evolutionary split some 2.6 million years ago. Still, the two species coexist in narrow transition zones between forest and savanna and can produce forest-savanna hybrids.

In order to study this mixing, Roca et al. have analyzed the nuclear and mitochondrial (mt) DNA of the two species across sub-Saharan Africa. The distribution of nuclear alleles is, as expected, distinct between the two elephant species; however, several of the savanna populations have mtDNA typical of their forest counterparts, even though their nuclear DNA is clearly of the savanna. This striking dichotomy between nuclear and maternally inherited mtDNA can best be explained by repeated hydridization between forest/hybrid females and the more aggressive savanna bulls, who presumably out-compete the forest/hybrid males, with each backcross further diluting the forest females' nuclear DNA. The high degree of similarity of the mtDNA in the savanna populations with that of the forest elephants suggests that the mixing is the result of a recent event, and the location of some of these savanna populations provides a clue: Although they are relatively distant from extant forests, they are within the range of the extended forests of the Holocene or, in the case of the Southern African populations, in the region of a large paleo-lake. — GR

Nature Genet. 37, 96 (2005).

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