Mitochondrial DNA panmixia in spiny lobster Palinurus gilchristi suggests a population expansion

The spiny lobster Palinurus gilchristi is endemic to the deep shelf waters along the southern coast of South Africa, where it supports a commercial fishery. Mark-recapture studies and phenotypic differences suggest there are 2 populations of this species along the coast, but it is unknown if the observed differences have arisen because of low gene flow and subsequent genetic differentiation. To investigate population structure and the physical processes that may have influenced gene flow, a portion of the mitochondrial DNA control region was sequenced for 187 lobsters across the entire range of the species. An analysis of molecular variance showed no significant genetic difference between the 2 putative populations. A mismatch distribution and Fu's F_S test indicated that this species has undergone a fairly recent demographic expansion (population size and geographic range). The genetic structure of this species could be panmictic due to a high amount of gene flow between the 2 regions during the larval stage, when the larvae are carried downstream by the Agulhas Current. Furthermore, the lack of genetic differences between the 2 putative populations could be the result of a recent demographic expansion accompanied by low diversity of haplotypes produced by a leading edge effect from the expansion.