Regional connectivity and viability selection in a range-expanding marine species

Identifying spatial and temporal patterns of connectivity among populations is fundamental to marine ecology, evolutionary biology, and fisheries management. Yet, due to large population sizes and low genetic differentiation among populations, empirical quantification of population connectivity across a species' entire range has not been achieved for an open-coast marine organism. Here, we leverage experimental transcriptomics to develop a genotyping-in-thousands by sequencing (GT-seq) panel to support assignment of recruits of the kelp forest gastropod, Kellet's whelk ( Kelletia kelletii ), collected across the species' biogeographic range. Over a three-year period, we identified high self-recruitment in the historical range (100%) and low self-recruitment in the expanded range (10.53 - 13.73%). Additionally, self-recruitment within the expanded range generally increased with recruit age, from 27.14% at 0.93 years to 43.40% at 1.93 years, indicating that the locally spawned individuals were more likely to survive to older ages than migrants from the historical range. Together, these results reveal limited self-recruitment in the expanded range and suggest that a post-settlement selective filter contributes to differential survival in a high gene flow marine system.