Deciphering genetic structure and inferring connectivity in marine species have been challenging due to weak genetic differentiation and limited resolution offered by traditional genotypic methods. The main goal of this study was to assess how a population genomics framework could help delineate the genetic structure of the American lobster (Homarus americanus) throughout much of the species’ range and increase the assignment success of individuals to their location of origin. We genotyped 10 156 filtered SNPs using RAD sequencing to delineate genetic structure and perform population assignment for 586 American lobsters collected in 17 locations distributed across a large portion of the species’ natural distribution range. Our results revealed the existence of a hierarchical genetic structure, first separating lobsters from the northern and southern part of the range (FCT = 0.0011; P-value = 0.0002) and then revealing a total of 11 genetically distinguishable populations (mean FST = 0.00185; CI: 0.0007–0.0021, P-value < 0.0002), providing strong evidence for weak, albeit fine-scale population structuring within each region. A resampling procedure showed that assignment success was highest with a subset of 3000 SNPs having the highest FST. Applying Anderson's (Molecular Ecology Resources, 2010, 10, 701) method to avoid ‘high-grading bias’, 94.2% and 80.8% of individuals were correctly assigned to their region and location of origin, respectively. Lastly, we showed that assignment success was positively associated with sample size. These results demonstrate that using a large number of SNPs improves fine-scale population structure delineation and population assignment success in a context of weak genetic structure. We discuss the implications of these findings for the conservation and management of highly connected marine species, particularly regarding the geographic scale of demographic independence.
Usage Notes:
10156 SNPs identified for Homarus americanus
VCF output of the 10156 SNPs identified for Homarus americanus through a RAD sequencing protocol.
10156-586.recode.vcf
8411snps-586ind
Data containing 8411 SNPs successfully genotyped in 586 lobsters.
8411-586.recode.vcf
FST_GEOGRAPHICAL_DISTANCES
Geographic distances and FST values between each pair of sampling location
Batch-catalogs for American lobster
batch_1.catalog.tags.tsv
Assignment results for 20 samples using THL method
assignment-20samples-regions.results.tsv
Assignment results for 36 samples using THL method
assignment-36samples-regions.results.tsv
Assignment results for 50 samples using THL method
assignment-50samples-regions.results.tsv
Assignment results for 100 samples using THL method
assignment-100samples-regions.results.tsv
Assignment results for the sites using LOO method (1 individual for ranking)
assignment.summary.stats.no.imputation.ranked-THL1-sites.tsv
Assignment results for regions using THL method (50% of individuals)
assignment.summary.stats.no.imputation.ranked-regions-THL0.5.tsv
Assignment results for sites using THL method (50% of individuals)
assignment.summary.stats.no.imputation.ranked-sites-THL0.5.tsv