Meeting Abstract
It can be difficult to resolve the balance between local adaptation and the opposing forces of gene flow and genetic drift, especially in marine invertebrates that can have extensive dispersal and fluctuating population sizes. The intertidal snail Chlorostoma funebralis has pelagic larvae and previous work using mtDNA polymorphism reported no genetic population structure. Nevertheless, recent studies have documented differences in thermal tolerance and transcriptomic responses to heat stress between northern and southern California, USA, populations. To increase our understanding of the dynamics influencing adaptive divergence, we used double digest restriction site-associated DNA (ddRAD) sequencing to identify 2371 genome-wide, quality filtered single nucleotide polymorphism (SNP) loci for C. funebralis collected from three northern and three southern California sites (15 individuals from each population). Considering all SNP loci, there was no evidence for genetic differentiation (average FST = 0.0042). However, separate analysis of the top ten percentile of SNPs based on FST (164 loci, average FST = 0.11) shows clear differentiation between geographic regions. This SNP subset includes several loci involved in ubiquitin protein degradation. Furthermore, outlier tests revealed 34 loci putatively under divergent selection between northern and southern populations. Three of these annotated outliers are known or hypothesized to be involved in cytoplasmic stress granule formation. This study increases our understanding of the factors constraining local adaptation in marine organisms, while nevertheless suggesting that ecologically driven, strong differentiation can occur at some relevant loci, even in a species with pelagic larvae.
