Phylogeography of Leptasterias species relative to an estuarine outflow in the Pacific Northwest

Comparing the phylogeography of sympatric species complexes can provide evidence of shared responses to historic events. Leptasterias is a genus of brooding, low-dispersing sea stars comprising several cryptic species complexes found from California to Alaska. Assessing their response to environmental events may elucidate processes underlying their diversity. Prior phylogenetic work around the San Francisco Bay, California suggests an outflow-associated pattern of Leptasterias clade distributions. For comparison, we examined Leptasterias phylogeography in the San Juan Islands (SJI), Washington to assess the potential effects of low-salinity outflow from the Fraser River. Mitochondrial cytochrome oxidase 1 (COI) barcoding (n=268) confirmed three sympatric cryptic clades of Leptasterias in the SJI discussed in Foltz 2008: L. aequalis A (I. pusilla complex), L. aequalis B (L. aequalis complex), and L. hexactis C (L. hexactis complex). Fine-scale sampling in the SJI showed an association between Leptasterias spp. COI clade frequency distribution and habitat exposure to waves and estuarine outflow. Selective forces from stressors such as low-salinity plumes or wave exposure could be maintaining the clade distributions seen in this island archipelago. In California, clades within the L. pusilla complex dominated bay-proximal sites more frequently exposed to low-salinity plumes out of the San Francisco Bay. Similarly in the SJI, the L. pusilla complex dominated sites more frequently exposed to low-salinity plumes from the Fraser River, while L. aequalis and L. hexactis dominated more wave-exposed, marine sites. This study suggests that estuarine sources may influence spatial genetic variation among Leptasterias populations. This combined regional comparison o f the distribution o f cryptic Leptasterias lineages relative to large sources o f estuarine outflow confirms some effect o f low-salinity plumes and wave exposure. Spatial and temporal patterns seen related to estuarine features in California poses concern for Leptasterias populations in the SJI, and further regional work in the context o f local habitat is needed to expand upon these findings.