Dispersal potential and population genetic structure in the marine intertidal of the eastern North Pacific

Population genetic theory and empirical comparisons of sister and sympatric marine species show that life history traits related to dispersal, such as pelagic duration (PD), should affect the frequency and spatial scale of migration, and thus influence population genetic structure. However, recent global analyses have concluded that PD is poorly correlated with marine population genetic structure. Here, we identify and compare genetic structure between four pairs of synchronously diverging co-distributed (SDC) species, drawn from standardized analyses of eight eastern North Pacific rocky intertidal invertebrates and one macrophyte. We test two hypotheses: H-0, that species with similar dispersal potential have similar population genetic structure, and H-1, that species with higher dispersal potential have lower population genetic differentiation. We find that differences in census population size (N-c), fecundity (F), and PD are sufficient to explain measured differences in population genetic structure (phi(ST), D-EST) between SDC species. However, theoretical differences in migration potential, calculated as a function of N-c, F, and PD, exceed empirical differences in migration, suggesting important roles for genetic drift and natural selection in structuring marine populations in the eastern North Pacific. A quantitatively similar relationship between PD and F-ST has been calculated for co-distributed species from the Great Barrier Reef, suggesting that meta-analyses of SDC species may reveal general patterns in how species' traits and geographical variation interact to structure populations.