Selection and microevolution of coat pattern are cryptic in a wild population of sheep

Gratten, J., Pilkington, J. G., Brown, E. A., Clutton-Brock, T. H., Pemberton, J. M. and Slate, J. (2012) Selection and microevolution of coat pattern are cryptic in a wild population of sheep. Molecular Ecology, 21 12: 2977-2990. doi:10.1111/j.1365-294X.2012.05536.x

Author Gratten, J.
Pilkington, J. G.
Brown, E. A.
Clutton-Brock, T. H.
Pemberton, J. M.
Slate, J.
Title Selection and microevolution of coat pattern are cryptic in a wild population of sheep
Journal name Molecular Ecology   Check publisher's open access policy
ISSN 0962-1083
Publication date 2012-06
Sub-type Article (original research)
DOI 10.1111/j.1365-294X.2012.05536.x
Open Access Status
Volume 21
Issue 12
Start page 2977
End page 2990
Total pages 14
Place of publication Oxford, United Kingdom
Publisher Wiley-Blackwell Publishing
Collection year 2013
Language eng
Formatted abstract
Understanding the maintenance of genetic variation in natural populations is a core aim of evolutionary genetics. Insight can be gained by quantifying selection at the level of the genotype, as opposed to the phenotype. Here, we show that in a natural population of Soay sheep which is polymorphic for coat pattern, recessive genetic variants at the causal gene, agouti signalling protein (ASIP) are associated with reduced lifetime fitness. This was due primarily to a reduction in juvenile survival of uniformly coloured (self-type) sheep, which are homozygous recessive, and occurs despite significantly higher reproductive success in surviving self-type adults. Consistent with their relatively low fitness, we show that the frequency of self-type individuals has declined from 1985 to 2008. Remarkably though, the frequency of the underlying self-allele has increased, because the frequency of heterozygous individuals (who harbour the majority of all self-alleles) has increased. Indeed, the ratio of observed/expected heterozygous individuals has increased during the study, such that there is now a significant excess of heterozygotyes. By employing gene-dropping simulations, we show that microevolutionary trends in the frequency and excess of ASIP heterozygotes are too pronounced to be caused by genetic drift. Studying this polymorphism at the level of phenotype rather than underlying genotype would have failed to detect cryptic fitness differences. We would also have been unable to rule out genetic drift as an evolutionary force driving genetic change. This highlights the importance of resolving the underlying genetic basis of phenotypic variation in explaining evolutionary dynamics.
Keyword Agouti signalling protein
Colour pattern
Genetic drift
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Non HERDC
Queensland Brain Institute Publications
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Citation counts: TR Web of Science Citation Count  Cited 16 times in Thomson Reuters Web of Science Article | Citations
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