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.
Highlights
Environmental features play a primary role in defining range limits for many species, and in coastal marine systems distributional boundaries are narrowly concentrated over regions where currents converge, diverge, or form retention zones (Gaylord and Gaines 2000; Byers and Pringle 2006)
Two population genetic studies on mudflat species that lack planktonic larval development (Corophium volutator: Einfeldt and Addison 2013; Hediste diversicolor: Einfeldt et al 2014) suggest that there is little or no gene flow between the Bay of Fundy and the Gulf of Maine. These results are consistent with reduced connectivity across this major biogeographic break, both species were recently introduced from Europe and may show patterns of genetic subdivision arising from independent founder events (Einfeldt and Addison 2015)
By assessing the levels of genetic structure among species with high dispersal abilities, our results provide insight into the importance of dispersal limitation to the formation of the biogeographic break observed at the community level across the mouth of the Bay of Fundy
Summary
Environmental features play a primary role in defining range limits for many species, and in coastal marine systems distributional boundaries are narrowly concentrated over regions where currents converge, diverge, or form retention zones (Gaylord and Gaines 2000; Byers and Pringle 2006). Two population genetic studies on mudflat species that lack planktonic larval development (Corophium volutator: Einfeldt and Addison 2013; Hediste diversicolor: Einfeldt et al 2014) suggest that there is little or no gene flow between the Bay of Fundy and the Gulf of Maine. These results are consistent with reduced connectivity across this major biogeographic break, both species were recently introduced from Europe and may show patterns of genetic subdivision arising from independent founder events (Einfeldt and Addison 2015). Investigating species with high dispersal potential (i.e., species with pelagic larva) will help assess the degree to which the biogeographic break between the Bay of Fundy and the Gulf of Maine is a general feature limiting connectivity throughout the region
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