Data from: Phenotypic correlates of Clock gene variation in a wild blue tit population: evidence for a role in seasonal timing of reproduction

The timing of reproduction in birds varies considerably within populations and is often under strong natural selection. Individual timing within years is dependent on a range of environmental factors in addition to having an additive genetic basis. In vertebrates, an increasing amount is known about the molecular basis for variation in biological timing. The Clock gene includes a variable poly-glutamine (poly-Q) repeat influencing behaviour and physiology. Recent work in birds, fish and insects has demonstrated associations between Clock genotype and latitude across populations, which match latitudinal variation in breeding time. In this study, we investigated the phenotypic correlates of variation in Clock genotype within a single blue tit Cyanistes caeruleus population over two successive breeding seasons. In females, but not in males, we observed a general trend for birds with fewer poly-Q repeats to breed earlier in the season. Incubation duration was shorter in both females and males with fewer repeats at the polymorphic Clock locus. Poly-Q Clock allele-frequency was homogenously distributed within the study population and did not exhibit any consistent environment-related variation. We further tested for effects of Clock genotype on reproductive success and survival, and found that females with fewer poly-Q repeats produced a higher number of fledged offspring. Our results therefore suggest that (i) selection in females, but not in males, for fewer poly-Q repeats may be operating, (ii) the across-population associations in timing of breeding involving this locus might be linked to variation within populations, and (iii) the Clock gene might be involved in local adaptation to seasonal environments.鸟类的繁殖时机在种群内部存在显著差异，且往往受到强烈的自然选择作用。个体年度繁殖时机除受加性遗传基础调控外，还依赖于一系列环境因素。在脊椎动物中，学界对生物节律变异的分子机制已有愈发深入的认识。生物钟基因（Clock gene）包含一段可影响行为与生理状态的可变聚谷氨酰胺（poly-Q）重复序列。近期针对鸟类、鱼类与昆虫的研究表明，不同种群间的Clock基因型与纬度存在关联，该关联与繁殖时机的纬度梯度变异相契合。本研究以单个青山雀（Cyanistes caeruleus）种群为研究对象，在两个连续繁殖季内，探究了Clock基因型变异的表型相关性。我们观察到，仅在雌性个体中存在总体趋势：聚谷氨酰胺重复序列更少的个体，其繁殖季启动时间更早；雄性个体未呈现该规律。在该多态性Clock基因座上，携带较少重复序列的雌雄个体，其孵化时长均更短。本研究种群内，poly-Q型Clock等位基因频率分布均匀，未表现出与环境相关的一致性变异。我们进一步检测了Clock基因型对繁殖成功率与存活率的影响，发现携带较少聚谷氨酰胺重复序列的雌性个体，其出飞幼鸟的数量更多。综上，本研究结果表明：① 雌性个体可能正受到针对更少聚谷氨酰胺重复序列的自然选择，而雄性个体未受此选择；② 不同种群间与该基因座相关的繁殖时机关联，可能与种群内部的变异存在关联；③ Clock基因可能参与了种群对季节性环境的局部适应过程。