Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, New York, USA.
PLoS One. 2011;6(12):e28843. doi: 10.1371/journal.pone.0028843. Epub 2011 Dec 21.
Recent studies of several species have reported a latitudinal cline in the circadian clock gene, Clock, which influences rhythms in both physiology and behavior. Latitudinal variation in this gene may hence reflect local adaptation to seasonal variation. In some bird populations, there is also an among-individual association between Clock poly-Q genotype and clutch initiation date and incubation period. We examined Clock poly-Q allele variation in the Barn Swallow (Hirundo rustica), a species with a cosmopolitan geographic distribution and considerable variation in life-history traits that may be influenced by the circadian clock. We genotyped Barn Swallows from five populations (from three subspecies) and compared variation at the Clock locus to that at microsatellite loci and mitochondrial DNA (mtDNA). We found very low variation in the Clock poly-Q region, as >96% of individuals were homozygous, and the two other alleles at this locus were globally rare. Genetic differentiation based on the Clock poly-Q locus was not correlated with genetic differentiation based on either microsatellite loci or mtDNA sequences. Our results show that high diversity in Clock poly-Q is not general across avian species. The low Clock variation in the background of heterogeneity in microsatellite and mtDNA loci in Barn Swallows may be an outcome of stabilizing selection on the Clock locus.
最近对几个物种的研究报告称，生物钟基因 Clock 存在纬度梯度，该基因影响生理和行为节律。该基因的纬度变化可能反映了对季节性变化的局部适应。在一些鸟类群体中，Clock 多聚谷氨酰胺基因型与产蛋日期和孵化期之间也存在个体间的关联。我们在 Barn Swallow（Hirundo rustica）中检查了 Clock 多聚谷氨酰胺等位基因的变化，Barn Swallow 是一种具有全球地理分布的物种，其生活史特征存在很大差异，这些差异可能受到生物钟的影响。我们对来自五个种群（三个亚种）的 Barn Swallow 进行了基因分型，并将 Clock 基因座的变异与微卫星基因座和线粒体 DNA（mtDNA）的变异进行了比较。我们发现 Clock 多聚谷氨酰胺区域的变异非常低，因为 >96%的个体为纯合子，而该基因座的另外两个等位基因在全球范围内都很罕见。基于 Clock 多聚谷氨酰胺基因座的遗传分化与基于微卫星基因座或 mtDNA 序列的遗传分化无关。我们的研究结果表明，Clock 多聚谷氨酰胺的高多样性并非普遍存在于鸟类物种中。Barn Swallow 中微卫星和 mtDNA 基因座异质性背景下的 Clock 低变异性可能是 Clock 基因座稳定选择的结果。
