Population structuring in mountain zebras (Equus zebra):: The molecular consequences of divergent demographic histories

The endangered mountain zebra (Equus zebra) is endemic to the semi-arid inhospitable mountainous escarpments of southern Africa. The species is divided taxonomically into two geographically separated subspecies, each with differing recent population histories. In Namibia, Hartmann's mountain zebra (E. z. hartmannae) is common and occurs in large free-ranging populations, whereas in South Africa, prolonged hunting and habitat destruction over the last 300 years has decimated populations of the Cape mountain zebra (E. z. zebra). In this study, we investigate the consequences of these divergent demographic histories for population genetic diversity and structure. We also examine the phylogeographic relationship between the two taxonomic groups. Genetic information was obtained at 15 microsatellite loci for 291 individuals from a total of 10 populations as well as 445 bp of the mitochondrial control region sequence data from 77 individuals. Both model-based and standard analytical approaches were used to examine the data. Both types of marker returned levels of diversity and structure that were consistent with population history. Low genetic variation within individual Cape mountain zebra populations, the characteristic indicator of population fragmentation and drift, was offset by moderate variation in the entire E. z. zebra sample. This implies that higher levels of diversity still exist within the Cape mountain zebra gene pool. A management strategy that entailed the mixing of aboriginal populations is therefore advocated in order to halt the further loss of Cape mountain zebra genetic diversity. Allele frequencies in Hartmann's mountain zebra were relatively resilient to demographic fluctuations. Due to the high incidence of mitochondrial haplotype sharing between populations, the hypothesis that Cape and Hartmann's mountain zebra mitochondrial lineages were reciprocally monophyletic was not supported. However, the presence of private alleles at nuclear loci rendered the two subspecies genetically distinct evolutionary significant units.