Evidence for panmixia despite barriers to gene flow in the hooked mussel, Ischadium recurvum (Mytilidae; Brachidontinae) along the North American coastline

Abstract

The discovery of phylogeographic patterns within broadly distributed marine species can be particularly challenging because absolute physical barriers to dispersal can be inconspicuous. Genetic boundaries often lie where ocean currents meet, forming sharp physical and ecological gradients, which may act as barriers to successful migrants. In eastern North America, coastal species often show phylogeographic differentiation associated with two recognized genetic barriers: the Gulf/Atlantic and the Virginia/Carolina discontinuities. We examined 185 specimens of the intertidal hooked mussel Ischadium recurvum collected from 15 locations along the eastern coastline of North America to examine phylogeographic, migration and historical demographic patterns associated climate change associated with Pleistocene glacial patterns. Hypothesis testing using Bayes factors in Migrate-n rejected the presence of phylogeographic breaks consistent with either maritime discontinuity and favoured a panmictic population model. The migration rate from the Gulf to the Atlantic was approximately three times higher than the migration from the Atlantic to the Gulf whereas the Carolina–Virginia migration rates were nearly equal. The summary statistics (Tajima’s D, Fu’s Fs) were significant and the demographic analyses (mismatch distributions, Bayesian skyline plot) were consistent with patterns of population expansion following glacial retreat during the Pleistocene epoch.

Keywords:

• Mitochondrial DNA
• panmixia
• gene flow
• Ischadium recurvum

Acknowledgements

This work would not have been possible without the assistance in the collection and donation of samples from Jessica Lunt and Eve Galimany (Smithsonian Marine Station).

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Additional information

Funding

This work was funded by University of West Georgia Faculty Research Grants, Louise Stokes Alliances for Minority Participation, UWG-STEM Education Improvement Plan (SEEP), University of West Georgia Biology Department.