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History or current selection? A molecular analysis of 'area effects' in the land snail Cepaea nemoralis.

ABSTRACT: We have used molecular variation in microsatellite and mitochondrial DNA to throw light on the origins of enigmatic geographical patterns, known as 'area effects', in the shell polymorphisms of the land snail Cepaea nemoralis. Our aim was to assess the relative importance of recent selection and historical events in the formation of these patterns. On the Marlborough Downs in Wiltshire, England, the 'type locality' for area effects, the frequencies of microsatellites are significantly associated with the frequencies of alleles for shell banding. A less clear association is found between microsatellites and shell colour. Mitochondrial haplotypes show no significant relationships. Although the correlated geographical patterns could be the results of random genetic drift from an initially uniform array of populations, the magnitudes of the patterns, and of the correlations between them, seem too strong to have arisen by drift since the last glaciation. Our results suggest that invasions from refugia have been the most important factors in forming area effects.

SUBMITTER: Davison A

PROVIDER: S-EPMC1690693 | biostudies-literature | 2000 Jul

REPOSITORIES: biostudies-literature

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History or current selection? A molecular analysis of 'area effects' in the land snail Cepaea nemoralis.

Davison A A Clarke B B

Proceedings. Biological sciences 20000701 1451

We have used molecular variation in microsatellite and mitochondrial DNA to throw light on the origins of enigmatic geographical patterns, known as 'area effects', in the shell polymorphisms of the land snail Cepaea nemoralis. Our aim was to assess the relative importance of recent selection and historical events in the formation of these patterns. On the Marlborough Downs in Wiltshire, England, the 'type locality' for area effects, the frequencies of microsatellites are significantly associated ...[more]

PMID: 10983823

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Project description:BACKGROUND: With a diversity of pigmented shell morphotypes governed by Mendelian patterns of inheritance, the common grove snail, Cepaea nemoralis, has served as a model for evolutionary biologists and population geneticists for decades. Surprisingly, the molecular mechanisms by which C. nemoralis generates this pigmented shelled diversity, and the degree of evolutionary conservation present between molluscan shell-forming proteomes, remain unknown. RESULTS: Here, using next generation sequencing and high throughput proteomics, we identify and characterize the major proteinaceous components of the C. nemoralis shell, the first shell-proteome for a pulmonate mollusc. The recent availability of several marine molluscan shell-proteomes, and the dataset we report here, allow us to identify 59 evolutionarily conserved and novel shell-forming proteins. While the C. nemoralis dataset is dominated by proteins that share little to no similarity with proteins in public databases, almost half of it shares similarity with proteins present in other molluscan shells. In addition, we could not find any indication that a protein (or class of proteins) is directly associated with shell pigmentation in C. nemoralis. This is in contrast to the only other partially characterized molluscan-shell pigmentation mechanism employed by the tropical abalone Haliotis asinina. CONCLUSIONS: The unique pulmonate shell-forming proteome that we report here reveals an abundance of both mollusc-specific and pulmonate-specific proteins, suggesting that novel coding sequences, and/or the extensive divergence of these sequences from ancestral sequences, supported the innovation of new shell types within the Conchifera. In addition, we report here the first evidence that molluscs use independently evolved mechanisms to pigment their shells. This proteome provides a solid foundation from which further studies aimed at the functional characterization of these shell-forming proteins can be conducted.

Dataset Information

History or current selection? A molecular analysis of 'area effects' in the land snail Cepaea nemoralis.

Publications

History or current selection? A molecular analysis of 'area effects' in the land snail Cepaea nemoralis.

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