Genetic-environment associations are increasingly revealed through population genomic data and can occur through a number of processes, including secondary contact, divergent natural selection, or isolation-by-distance. Here we investigate the influence of the environment, including seasonal temperature and salinity, on the population structure of the invasive European green crab (Carcinus maenas) in eastern North America. Green crab populations in eastern North America are associated with two independent invasions, previously shown to consist of distinct northern and southern ecotypes, with a contact zone in southern Nova Scotia, Canada. Using a RAD-seq panel of 9137 genome-wide SNPs, we detected 41 SNPs (0.49%) whose allele frequencies were highly correlated with environmental data. A principal components analysis of 25 environmental variables differentiated populations into northern, southern, and admixed sites in concordance with the observed genomic spatial structure. Furthermore, a spatial principal components analysis conducted on genomic and geographic data revealed a high degree of global structure (p<0.0001) partitioning a northern and southern ecotype. Redundancy and partial redundancy analyses revealed that among the environmental variables tested, winter sea surface temperature had the strongest association with spatial structuring, suggesting that it is an important factor defining range and expansion limits of each ecotype. Understanding environmental thresholds associated with intraspecific diversity will facilitate the ability to manage current and predict future distributions of this aquatic invasive species.
Usage Notes:
Crab_Genepop_EnvironmentalOutliers
A genepop file of green crab genotypes containing only SNPs identified as being correlated with environmental variables.
Crab_Genepop_EnvOutliers.txt
Neutral Genotypes
Genepop file of neutral SNP genotypes
Neutral_GP.txt
GreenCrabEnvironmentalData
Environmental (temperature and salinity) data, and Cartesian coordinates for each sample site in our study.
GreenCrabEnvData.csv
CrabCoordinates
Coordinates for the sample locations, plus transformed Cartesian coordinates.