Avian Clock gene polymorphism: evidence for a latitudinal cline in allele frequencies

Abstract

In comparison with most animal behaviours, circadian rhythms have a well‐characterized molecular genetic basis. Detailed studies of circadian clock genes in ‘model’ organisms provide a foundation for interpreting the functional and evolutionary significance of polymorphic circadian clock genes found within free‐living animal populations. Here, we describe allelic variation in a region of the avian Clock orthologue which encodes a functionally significant polyglutamine repeat ( Clk polyQcds), within free‐living populations of two passerine birds, the migratory bluethroat ( Luscinia svecica ) and the predominantly nonmigratory blue tit ( Cyanistes caeruleus ). Multiple Clk polyQcds alleles were found within populations of both species (bluethroat: 12 populations, 7 alleles; blue tit: 14 populations, 9 alleles). Some populations of both species were differentiated at the Clk polyQcds locus as measured by F ST and R ST values. Among the blue tit, but not bluethroat populations, we found evidence of latitudinal clines in (i) mean Clk polyQcds repeat length, and (ii) the proportions of three Clk polyQcds genotype groupings. Parallel analyses of microsatellite allele frequencies, which are considered to reflect selectively neutral processes, indicate that interpopulation allele frequency variation at the Clk polyQcds and microsatellite loci does not reflect the same underlying demographic processes. The possibility that the observed interpopulation Clk polyQcds allele frequency variation is, at least in part, maintained by selection for microevolutionary adaptation to photoperiodic parameters correlated with latitude warrants further study.

Bibliographic Information