RAD‐Seq derived markers flank the shell colour and banding loci of the Cepaea nemoralis supergene

Abstract

Studies on the classic shell colour and banding polymorphism of the land snail C epaea played a crucial role in establishing the importance of natural selection in maintaining morphological variation. Cepaea is also a pre‐eminent model for ecological genetics because the outward colour and banding phenotype is entirely genetically determined, primarily by a ‘supergene’ of at least five loci. Unfortunately, progress in understanding the evolution and maintenance of the C epaea polymorphism stalled, partly because of a lack of genetic markers. With a view to re‐establish C epaea as a prominent model of molecular ecology, we made six laboratory crosses of C epaea nemoralis , five of which segregated for shell ground colour ( C ) and the presence or absence of bands ( B ). First, scoring of colour and banding in 323 individuals found no recombination between the C and B loci of the supergene. Second, using restriction site–associated DNA sequencing ( RAD ‐ S eq) of two parents and 22 offspring, we identified 44 anonymous markers putatively linked to the colour ( C ) and banding ( B ) loci. The genotype of eleven of the most promising RAD ‐ S eq markers was independently validated in the same 22 offspring, then up to a further 146 offspring were genotyped. The closest RAD ‐ S eq markers scored are within ~0.6 centimorgan (cM) of the C ‐ B supergene linkage group, with the combined loci together forming a 35.8 cM linkage map of markers that flank both sides of the C epaea C ‐ B supergene.

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