Low reproductive isolation and highly variable levels of gene flow reveal limited progress towards speciation between European river and brook lampreys.
Ecologically based divergent selection is a factor that could drive reproductive isolation even in the presence of gene flow. Population pairs arrayed along a continuum of divergence provide a good opportunity to address this issue. Here, we used a combination of mating trials, experimental crosses and population genetic analyses to investigate the evolution of reproductive isolation between two closely related species of lampreys with distinct life histories. We used microsatellite markers to genotype over 1000 individuals of the migratory parasitic river lamprey (Lampetra fluviatilis) and freshwater-resident nonparasitic brook lamprey (Lampetra planeri) distributed in 10 sympatric and parapatric population pairs in France. Mating trials, parentage analyses and artificial fertilizations demonstrated a low level of reproductive isolation between species even though size-assortative mating may contribute to isolation. Most parapatric population pairs were strongly differentiated due to the joint effects of geographic distance and barriers to migration. In contrast, we found variable levels of gene flow between sympatric populations ranging from panmixia to moderate differentiation, which indicates a gradient of divergence with some population pairs that may correspond to alternative morphs or ecotypes of a single species and others that remain partially isolated. Ecologically based divergent selection may explain these variable levels of divergence among sympatric population pairs, but incomplete genome swamping following secondary contact could have also played a role. Overall, this study illustrates how highly differentiated phenotypes can be maintained despite high levels of gene flow that limit the progress towards speciation.
UMR 985 Ecologie et Santé des Ecosystèmes, INRA, Rennes, France.|UMR ESE, Agrocampus Ouest, Rennes, France.
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Rougemont
UMR 985 Ecologie et Santé des Ecosystèmes, INRA, Rennes, France.|UMR ESE, Agrocampus Ouest, Rennes, France.|Laboratory for Conservation Biology, Department of Ecology and Evolution, University of Lausanne, Biophore, Switzerland.
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Gaigher
Muséum National d'Histoire Naturelle, CRESCO, Dinard, France.|UMR CARRTEL, INRA, Thonon-les-Bains, France.
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Lasne
UMR 985 Ecologie et Santé des Ecosystèmes, INRA, Rennes, France.|UMR ESE, Agrocampus Ouest, Rennes, France.
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Côte
Unité Expérimentale d'Ecologie et d'Ecotoxicologie Aquatique, INRA, Rennes, France.
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Coke
UMR 985 Ecologie et Santé des Ecosystèmes, INRA, Rennes, France.|UMR ESE, Agrocampus Ouest, Rennes, France.
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Besnard
UMR 985 Ecologie et Santé des Ecosystèmes, INRA, Rennes, France.|UMR ESE, Agrocampus Ouest, Rennes, France.
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Launey
UMR 985 Ecologie et Santé des Ecosystèmes, INRA, Rennes, France.|UMR ESE, Agrocampus Ouest, Rennes, France.
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Evanno
D000818:Animals; D001499:Bayes Theorem; D016000:Cluster Analysis; D051456:Gene Flow; D005819:Genetic Markers; D007798:Lampreys / Q000145:classification / Q000235:genetics / Q000502:physiology*; D018895:Microsatellite Repeats / Q000235:genetics; D012098:Reproduction; D013045:Species Specificity
D005819:Genetic Markers
Lampetra; genetic structure; life-history strategy; parapatry; reproductive barrier; sympatry