Genetic evidence for multiple dispersal mechanisms in a marine direct developer, Leptasterias sp. (Echinodermata: Asteroidea)

Abstract

Quantifying patterns of gene flow is critical for predicting the future resilience of local marine communities. Brooding species may be particularly susceptible to extirpation, as the lack of a pelagic larval phase may limit dispersal capacity and increase the risk of local extinction. Here, we investigate the population genetic structure of Leptasterias sp., a brooding sea star and important intertidal predator. Dispersal in this genus occurs primarily by crawling, but some have suggested that occasional “rafting” events can move individuals long distances. We used microsatellite markers to estimate genotypic variation across six collection sites of varying distances apart along the Oregon coast. We found evidence of strong population structure at the level of capes, and especially high divergence between two sites within Cape Blanco. Although cape-level genetic structure is broadly consistent with isolation-by-distance, additional mechanisms may be required to explain the elevated magnitude of genetic divergence on a finer scale. We propose that a known offshore water jet off Cape Blanco may act as phylogeographic barrier, hindering transport of rafting individuals from neighboring sites. This pattern suggests, indirectly, that rafting may be more important than previously appreciated in generating long-term genetic isolation between nearby sites. Our findings suggest that even for a sessile brooding species, connectivity and genetic structure can vary on a fine spatial scale and may be subject to environmental and oceanographic forces.