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变异，且往往受到强烈的自然选择作用。个体在同一年中的繁殖时机，除了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，人们对生物时序变异的分子基础已有越来越多的了解。生物钟基因（Clock）包含一段可变的聚谷氨酰胺（poly-glutamine, poly-Q）重复序列，该序列可影响动物的行为与生理机能。近期针对鸟类、鱼类与昆虫的研究已证实，不同种群的Clock基因型与纬度存在关联，这与繁殖时机的纬度梯度变异相吻合。本研究针对单个蓝山雀（Cyanistes caeruleus）种群，在两个连续的繁殖季中，探究了Clock基因型变异的表型关联。我们观察到，仅在雌性个体中存在普遍趋势：携带更少poly-Q重复序列的个体，其繁殖季起始时间更早。在该多态性Clock基因座上携带较少重复序列的个体，无论雌雄，其孵化时长均更短。该Clock基因的poly-Q等位基因频率在研究种群中呈均匀分布，未表现出任何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，结果发现，携带更少poly-Q重复序列的雌性个体，其出飞幼鸟的数量更多。因此，本研究结果表明：（1）可能存在针对雌性个体（而非雄性）更少poly-Q重复序列的选择作用；（2）该基因座相关的跨种群繁殖时机关联，可能与种群内部的变异存在联系；（3）生物钟基因（Clock）可能参与了种群对季节性环境的局部适应过程。