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Strong population differentiation of softshell clams (Mya arenaria) sampled across seven biogeographic marine ecoregions: possible selection and isolation by distance

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Abstract

Twenty-two Mya arenaria samples spanning seven marine ecoregions mostly situated in the Cold Temperate Northwest Atlantic (CTNA) biogeographic province were collected between 2001 and 2010 and genotyped at seven highly polymorphic microsatellite loci to test for population differentiation. Results showed strong regional differentiation with six genetic clusters: (1) Northern Gulf of St. Lawrence (GSL), (2) Magdalen Archipelago, (3) Southern GSL, (4) Lower Atlantic Canada, (5) US Coasts and (6) Northern Europe. Population structure was supported no matter the statistical approach and generally does not reflect the geographical limits of marine ecoregions. A latitudinal cline in allelic richness provides evidence for a northward post-glacial expansion range for this species. While geographical distance explains the genetic variation detected in southern CTNA, increased heterogeneity observed in northern CTNA can be explained by isolation by distance, marine landscaping and presumable selective processes acting at the Mar5 locus. Exclusion of Mar5 from analyses resulted in the detection of three genetic clusters instead of six.

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Acknowledgments

Authors wish to thank the following people for their much appreciated help in the field and in the laboratory: Éric Parent, Éric Tremblay, Léophane Leblanc, Firmin Leblanc, Gilles Miron, Julie Quimper, Alexandra Valentin, Philippe Galipeau, Chantale Daigle, Carole Degrâce, Andre Siah, Sylvie Brulotte, Patrice Pelletier, the Kouchibouguac, Kejimkujik and Cape Breton Highlands National Parks and the Atlantic Veterinary College. Authors would also like to thank all anonymous reviewers who commented on earlier drafts of the manuscript. This study was funded by the Aquaculture Collaborative Research and Development Program (ACRDP), the National Sciences and Engineering Research Council of Canada (NSERC) and the Réseau Aquaculture du Québec (RAQ) grants to P. St-Onge, J.M. Sévigny and R. Tremblay.

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  1. Institut des Sciences de la Mer, Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, QC, G5L 3A1, Canada

    Philippe St-Onge & Réjean Tremblay

  2. Institut Maurice-Lamontagne, Pêches et Océans Canada, 850 Route de la Mer, Mont-Joli, QC, G5H 3Z4, Canada

    Jean-Marie Sévigny

  3. UC Curation Center, University of California Office of the President, 415 20th Street, Oakland, CA, 94612, USA

    Carly Strasser

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  1. Philippe St-Onge
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Correspondence to Philippe St-Onge.

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Communicated by T. Reusch.

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Online Resource 9 Assessment of the most probable number of clusters (K) explaining the genetic structure of M. arenaria individuals (N = 604) from 22 samples genotyped with seven microsatellite loci as detected with the ΔK graphical method developed by Evanno et al. (2005). a) Mean (±SD; N = 4) posterior probability of data; b) mean rate (±SD; N = 4) of change of the likelihood distribution; c) mean (±SD; N = 4) absolute values of the second-order rate of change of the likelihood distribution; d) ΔK. Arrows point to the greatest value of ΔK and the most probable number of clusters (K = 6) explaining the genetic structure in the dataset (DOCX 138 kb)

227_2012_2157_MOESM10_ESM.docx

Online Resource 10 Assessment of the most probable number of clusters (K) explaining the genetic structure of M. arenaria individuals (N = 604) from 22 samples genotyped with six microsatellite loci (all but Mar5) as detected with the ΔK graphical method developed by Evanno et al. (2005). a) Mean (±SD; N = 4) posterior probability of data; b) mean rate (±SD; N = 4) of change of the likelihood distribution; c) mean (±SD; N = 4) absolute values of the second-order rate of change of the likelihood distribution; d) ΔK. Arrows point to the greatest value of ΔK and the most probable number of clusters (K = 3) explaining the genetic structure in the dataset (DOCX 186 kb)

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St-Onge, P., Sévigny, JM., Strasser, C. et al. Strong population differentiation of softshell clams (Mya arenaria) sampled across seven biogeographic marine ecoregions: possible selection and isolation by distance. Mar Biol 160, 1065–1081 (2013). https://doi.org/10.1007/s00227-012-2157-5

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