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Richards, Paul M. and Liu, M. Maureen and Lowe, Natalie and Davey, John W. and Blaxter, Mark L. and Davison, Angus (2013) RAD-Seq derived markers flank the shell colour and banding loci of the Cepaea nemoralis supergene. Molecular Ecology, 22 (11). pp. 3077-3089. ISSN 0962-1083

Abstract

Studies on the classic shell colour and banding polymorphism of the land snail Cepaea

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 Cepaea polymorphism stalled,

partly because of a lack of genetic markers. With a view to re-establish Cepaea as a

prominent model of molecular ecology, we made six laboratory crosses of Cepaea

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-Seq) 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-Seq markers was independently

validated in the same 22 offspring, then up to a further 146 offspring were genotyped.

The closest RAD-Seq 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 Cepaea C-B supergene.

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