Genetic discontinuity in two high dispersal marine invertebrates in the northwest Atlantic

Abstract

Oceanic circulation patterns shape both the distribution of species and spatial patterns of intraspecific genetic variation by influencing passively dispersed marine invertebrates. In the northwest Atlantic, strong and consistent currents at the mouth of the Bay of Fundy are expected to restrict dispersal in this region, but the relationship between populations of high dispersal species along the surrounding coastal regions has been largely underrepresented in the phylogeographic literature. We analyzed phylogeographic patterns in two intertidal invertebrates with high dispersal abilities, Tritia obsoleta (Mollusca: Gastropoda) and Macoma petalum (Mollusca: Bivalvia), between Cape Cod and the Gulf of St. Lawrence using mitochondrial DNA (mtDNA). Hierarchical analysis of molecular variance revealed population structuring among regions defined by circulation patterns, highly divergent lineages within M. petalum, and strong concordant genetic subdivision in both species between the Bay of Fundy and Gulf of Maine. Our results suggest that the gyre at the mouth of the bay is influential in restricting alongshore dispersal, allowing genetic divergence between regions to arise through genetic drift. These findings are concordant with biogeographic and phylogeographic studies of other marine organisms, suggesting that the genetic isolation of widely distributed species may be a common feature of intertidal invertebrate communities in the Bay of Fundy.

Genotype by sequencing identifies natural selection as a driver of intraspecific divergence in Atlantic populations of the high dispersal marine invertebrate, Macoma petalum

“…Our results are broadly consistent with analyses of mtDNA sampled from the same individuals (Einfeldt et al., ). We detected greater pairwise F ST among the northern populations (GSL and NS) than those sampled in the Bay of Fundy and Gulf of Maine (Table ), suggesting that higher levels of gene flow connect populations in the south.…”

“…We detected a strong genetic break in the Atlantic population of M. petalum between the Bay of Fundy and the Gulf of Maine using putatively selected SNPs (outlier loci). Previous analysis of mtDNA in M. petalum showed hierarchical structure among four broad geographic regions (GOM, BF, NS, and GSL) for this species as well as the presence of a phylogeographic break at the Bay of Fundy (Einfeldt et al., ; Figures and ). While we failed to detect similar patterns of hierarchical structure among regions in our data, neutral SNPs showed a clear, but weak, pattern of isolation across the biogeographic break, suggesting some limitation in gene flow between the Bay of Fundy and Gulf of Maine.…”

“…Circular currents are known to prevent mixing (White et al., ). Therefore, the EMCC likely minimizes gene flow between the Bay of Fundy and the Gulf of Maine, as seen in C. volutator , H. diversicolor , and T. obsoleta (Einfeldt & Addison, ; Einfeldt et al., , ). Tilburg et al.…”

“…We checked the quality of extracted DNA by running an aliquot on a 1% agarose gel for UV imaging and measuring concentration with the QUIBIT 2.0 Fluorometer Broad Range assay (Invitrogen). Mitochondrial sequences from previous analysis of the same individuals were used to confirm that all individuals were indeed M. petalum and not M. balthica as M. balthica 's range extends into the Gulf of Saint Lawrence (Einfeldt et al., ).…”

“…Pie charts represent the frequency of mt DNA haplotypes (704‐bp COI / COIII , n = 194) from each site belonging to the four main lineages described in Einfeldt et al. (). Eastern Maine Coastal Current ( EMCC ) and the Western Maine Coastal Current ( WMCC ) are indicated, and all current patterns are adapted from Aretxabaleta et al.…”