Testing dispersal limits in the sea: range-wide phylogeography of the pronghorn spiny lobster Panulirus penicillatus

Aim To resolve phylogeographical partitions in the pronghorn spiny lobster, Panulirus penicillatus, which has a nine-month pelagic larval phase and the broadest distribution among spiny lobsters. With samples from the Red Sea to the East Pacific, we test genetic partitions across two-thirds of the planet, in a species with one of the longest pelagic phases. Location Red Sea, Indian and Pacific Oceans. Methods A fragment of the mtDNA cytochrome c oxidase subunit I gene (COI) was resolved in 774 individuals from 28 locations, plus 55 sequences (10 locations) from public databases. Portions of COI, 12S and 16S mtDNA regions were resolved for phylogenetic analyses on a subset of individuals. Phylogenetic and population-level analyses were used to detect evolutionary partitions and dispersal barriers. Results Significant population structuring was detected (overall Phi(ST) = 0.310, P < 0.001). Samples from the Red Sea and East Pacific Provinces (western and eastern range edges) comprise distinct phylogenetic lineages, divergent at d = 1.1% and 1.8%, respectively, from the Indo-Pacific. Coalescent analyses indicate a Pleistocene isolation for the Red Sea (0.71 Ma) and East Pacific (1.52 Ma). Excluding the Red Sea and East Pacific, structure across the rest of the range was comparatively low, but significant (Phi(ST) = 0.018, P < 0.001). Main conclusions The Red Sea and East Pacific populations are phylogenetically distinct from populations elsewhere in the range. The East Pacific population diverged earliest, and may represent a distinct subspecies. Phylogeographical divisions align with the major Indo-Pacific biogeographical barriers, and with subsets of provincial designations from two frameworks: one based on levels of endemism and one on species composition. Tropical and temperate regions in the Pacific are significantly differentiated, potentially indicating an ecological partition. Isolation at eastern and western peripheral provinces may serve as a starting point for evolutionary diversification within this group.