Speciation and Population Genetic Structure in Tropical Pacific Sea Urchins

Abstract

Abstract.-Unlike populations of many terrestrial species, marine populations often are not separated by obvious, permanent barriers to gene flow. When species have high dispersal potential and few barriers to gene flow, allopatric divergence is slow. Nevertheless, many marine species are of recent origin, even in taxa with high dispersal potential. To understand the relationship between genetic structure and recent species formation in high dispersal taxa, we examined population genetic structure among four species of sea urchins in the tropical Indo-West Pacific that have speciated within the past one to three million years. Despite high potential for gene flow, mtDNA sequence variation among 200 individuals of four species in the urchin genus Echinometra shows a signal of strong geographic effects. These effects include (1) substantial population heterogeneity; (2) lower genetic variation in peripheral populations; and (3) isolation by distance. These geographic patterns are especially strong across scales of 5000-10,000 km, and are weaker over scales of 2500-5000 km. As a result, strong geographic patterns would not have been readily visible except over the wide expanse of the tropical Pacific. Surface currents in the Pacific do not explain patterns of gene flow any better than do patterns of simple spatial proximity. Finally, populations of each species tend to group into large mtDNA regions with similar mtDNA haplotypes, but these regional boundaries are not concordant in different species. These results show that all four species have accumulated mtDNA differences over similar spatial and temporal scales but that the precise geographic pattern of genetic differentiation varies for each species. These geographic patterns appear much less deterministic than in other well-known coastal marine systems and may be driven by chance and historical accident.

High genetic diversities and complex genetic structure in an Indo-Pacific tropical reef fish (Chlorurus sordidus): evidence of an unstable evolutionary past?

“…This suggests that the significant effect of IBD across the species range was a result of complete isolation of the WIO populations rather than a gradual dilution of settlement events with increasing geographical distance. This pattern is similar to that found among pelagic larval dispersing marine organisms, which generally show signs of IBD only at the largest spatial scales (Richardson 1983;Palumbi et al 1997;Planes and Fauvelot 2002).…”

High gene flow due to pelagic larval dispersal among South Pacific archipelagos in two amphidromous gastropods (Neritomorpha: Neritidae)

“…Genetic structure or divergence across the large expanses of open water (B2000 km) that lie between archipelagos in the Western and Central Pacific, such as what we found in N. canalis, is commonly observed in marine species (Palumbi et al, 1997;Bernardi et al, 2001;Lessios et al, 2001;Crandall et al, 2008) as well as in an amphidromous goby (Keith et al, 2005). It is therefore remarkable that N. dilatatus shows no evidence of genetic structure across this span.…”

Current patterns, habitat discontinuities and population genetic structure: the case of the kelp Laminaria digitata in the English Channel

“…seagrass: Bandeira & Nilsson 2001;bryozoans: Goldson et al 2001;fish: Rocha-Olivares & Vetter 1999), other studies have found no correlation (echinoderms: Palumbi et al 1997;reef fishes: Shulman & Bermingham 1995). In this study, 2 major reasons may explain the absence of current/gene flow correlation of Laminaria digitata in the English Channel.…”