Publication Date:
2012-09-26
Description:
Estimates of the proportion of amino acid substitutions that have been fixed by selection ( α ) vary widely among taxa, ranging from zero in humans to over 50% in Drosophila . This wide range may reflect differences in the efficacy of selection due to differences in the effective population size ( N e ). However, most comparisons have been made among distantly related organisms that differ not only in N e but also in many other aspects of their biology. Here, we estimate α in three closely related lineages of house mice that have a similar ecology but differ widely in N e : Mus musculus musculus ( N e ~ 25,000–120,000), M. m. domesticus ( N e ~ 58,000–200,000), and M. m. castaneus ( N e ~ 200,000–733,000). Mice were genotyped using a high-density single nucleotide polymorphism array, and the proportions of replacement and silent mutations within subspecies were compared with those fixed between each subspecies and an outgroup, Mus spretus . There was significant evidence of positive selection in M. m. castaneus , the lineage with the largest N e , with α estimated to be approximately 40%. In contrast, estimates of α for M. m. domesticus ( α = 13%) and for M. m. musculus ( α = 12 %) were much smaller. Interestingly, the higher estimate of α for M. m. castaneus appears to reflect not only more adaptive fixations but also more effective purifying selection. These results support the hypothesis that differences in N e contribute to differences among species in the efficacy of selection.
Print ISSN:
0737-4038
Electronic ISSN:
1537-1719
Topics:
Biology
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