Phylogeography of the flag cabrilla Epinephelus labriformis (Serranidae): implications for the biogeography of the Tropical Eastern Pacific and the early stages of speciation in a marine shore fish

Aim To examine the role of previously described biogeographical boundaries in shaping phylogeographical relationships within and among two putative eastern Pacific sibling species, the flag cabrilla, Epinephelus labriformis and the Clipperton grouper, Epinephelus clippertonensis (Serranidae). Location Tropical Eastern Pacific (TEP). Methods Sequence data from the mitochondrial cytochrome b gene were obtained from samples throughout the range of the species. Coalescence analysis, mismatch distributions and an analysis of molecular variance (AMOVA) were used to infer population differentiation. Results Overall, 49 haplotypes were found among 304 specimens, and there was significant structure corresponding to geographical locality (AMOVA,$\Phi_{ct} = 0.198$, P < 0.001;$\Phi_{st} = 0.207$, P < 0.001;$F_{st} = 0.169$, P < 0.001;$F_{ct} = 0.151$, p = 0.036). Coalescence analysis indicates a population expansion at Clipperton Atoll during the mid-Pleistocene. Main conclusions Our results suggest that previously described barriers to dispersal along the mainland of the TEP may not impinge on the dispersal ability of marine species, such as these groupers, that have long-lived pelagic larvae. In contrast, gene flow between mainland and island populations of the readily distinguishable morphospecies E. labriformis and E. clippertonensis is restricted. The low level of genetic differentiation between the two species indicates that changes in external colour patterns may evolve more rapidly than genetic markers commonly used to delimit species boundaries. Thus a combination of colour differences and a lack of reciprocal monophyly may act as good indicators of incipient speciation in the marine environment.