Differences in spatial genetic population structure between African and Asian elephant (Loxodonta africana, Elephas maximus) as revealed by sequence analysis of the mitochondrial Cyt b gene

Abstract

To assess spatial genetic population structure of both extant elephant species, we investigated sequence variation in 369bp of the mitochondrial Cyt b gene in 23 specimens of African elephant Loxodonta africana (Blumenbach, 1797) from three regions in the Southern part of Africa. In an integrated analysis, these results were compared to data of a previous study, where the same gene region had been analysed in 53 Asian elephants Elephas maximus (Linnaeus, 1758) from 5 different regions on Sri Lanka and Asian mainland. In Loxodonta, 14 polymorphic sites defined 6 different mitochondrial haplotypes with a mean sequence divergence of 2.085%. In Elephas, 6 polymorphic sites defined 8 different haplotypes with a mean sequence divergence of 0.942%. Compared to other mammals, genetic variation is high in Loxodonta and moderate in Elephas. The difference in genetic variation among the species could be explained either by a Pliocene bottleneck in Elephas or by different long term effective population sizes. In Elephas, a star like phylogeny of haplotypes was found, indicative of a population expansion after a bottleneck. In Loxodonta, very divergent mtDNA lineages coexisted, suggesting the absence of any bottleneck in population history. Within regional subpopulations, both species showed similar mean haplotype diversities, while mean nucleotide diversity within regions was higher in Loxodonta than in Elephas. This suggest larger long-term effective population sizes in Loxodonta, while short-term effective population sizes are presumably similar in both species. Spatial genetic population structure in Loxodonta is mainly determined by isolation-by--distance, while in Elephas it is impacted by human translocation. Human translocation might have prevented isolated small Elephas populations from severe genetic depletion.