Discovery of populations endemic to a marine biogeographical transition zone

AimBiogeographical transition zones are areas of overlap between the faunas of adjacent biogeographical entities. Particularly, the well-defined transition zones along linear coastlines are interesting natural laboratories to study dispersal and incipient speciation. Few studies have explored whether marine biogeographical transition zones harbour biodiversity that is distinct from that of the biogeographical entities they separate. The Wild Coast in eastern South Africa is a poorly-studied transition zone between regions warm-temperate and subtropical faunas, and is generally considered to be an area of faunal overlap. LocationThe South African portion of the Western Indian Ocean MethodsSequences of the DNA barcoding marker COI were generated from 306 estuarine sandprawns (Callichirus kraussi) collected at 13 sites. Genetic structure and evolutionary history were assessed using a haplotype network and a Bayesian discrete phylogeographic analysis. ResultTwo populations were identified whose ranges are centred on the Wild Coast, a rare one in the northern portion and a more common one in the central and southern portion of this biogeographical transition zone. These populations are not closely related to each other, but descend from subtropical and warm-temperate sister populations, respectively. ConclusionsThis is the first study to indicate that the Wild Coast marine biogeographical transition zone is not merely an area of faunal overlap, and one of very few studies to have discovered genetically unique populations within a marine biogeographical transition zone. The Wild Coast may harbour additional unique biodiversity that remains to be discovered, including rare species that require protection. More research is required to understand how this environmentally dynamic marine biogeographical transition zone differs from the adjacent biogeographical provinces.