Temporal and spatial variation in population structure and distribution of a direct-developing cryptic species complex, Leptasterias

Temporal genetic studies of direct developing organisms are rare. Marine invertebrates lacking a planktonic larval stage are expected to have lower dispersal, low gene flow, and a higher potential for local adaptation than organisms with planktonic dispersal. Leptasterias is a genus of brooding sea stars that contains several cryptic species complexes. Population genetic methods were used to resolve patterns of fine-scale population structure in central California Leptasterias using three loci from nuclear and mitochondrial genomes. Historic samples were compared to contemporary samples to delineate changes in species distributions in space and time. Contemporary sampling confirmed a pattern of shared haplotypes at both mitochondrial and nuclear loci around the mouth of San Francisco Bay with distinct, shared haplotypes bracketing populations north and south of the bay. Phylogenetic analysis confirmed the presence of a baylocalized clade and revealed the presence of an additional bay-localized and previously undescribed clade of Leptasterias. Analysis of contemporary and historic samples indicated these two clades may be experiencing a constriction in their southern range limit and suggest a decrease in abundance at sites at which they were once prevalent. Historic sampling revealed a different distribution of diversity along the California coastline compared to contemporary sampling and illustrates the importance of temporal genetic sampling in phylogeographic studies.