Genetic variation of the forest elephant Loxodonta africana cyclotis across Central Africa

Doctoral thesis English OPEN
Johnson-Bawe, Mireille
  • Subject: QH301

The first comprehensive genetic study of central African forest elephants (CAEs) is presented here based on mitochondrial DNA (mtDNA) and nuclear microsatellite loci. MtDNA analysis revealed low genetic divergence between most groups. Haplotype distribution was not correlated with geographical localities, indicating high levels of gene flow. Two divergent haplogroups, illustrated by a bimodal distribution of pairwise differences in the control region, implies that secondary contact and ongoing introgression has occurred between populations expanding from at least two putative glacial refugia. Similarly, microsatellite analysis revealed low genetic differentiation among sites, suggesting high levels of gene flow as well as regional admixture with two genetically-based clusters inferred from Bayesian analyses. It is important to note through, that although both mtDNA and microsatellites identified two groups or genetic clusters, assignment of individuals to these clusters was not consistent across genomes possibly a result of differential admixture in nuclear and mitochondrial DNA. No correlation was found between genetic and geographical distances for both genomes. Previous phylogenetic analyses, using either on genetic or morphological characters, were based on a very limited number of forest elephant samples. A large-scale reassessment of mitochondrial DNA diversity in CAEs compared to published data on both forest and savannah forms revealed a complex phylogeographic history for African elephants, and an evolutionary trajectory more complex than prevailing two-taxon models have assumed. Mitochondrial control region and Cytochrome b sequences were analysed for CAEs and compared to other African elephant data. CAE populations fell into at least two lineages with West African elephants (both forest and savannah) sharing their mitochondrial history almost exclusively with Central African forest elephants. Extant African elephant populations therefore seem to have originated from multiple refugia lineages that have subsequently undergone introgression. Thus, the complex phylogeographic history of African elephants does not support a simple two-taxon model and management strategies incorporating the two-taxa model could be misinformed until further data give clarifies the origins of elephant populations throughout Africa
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