Data from: Asynchrony of seasons: genetic differentiation associated with geographic variation in climatic seasonality and reproductive phenology

Many organisms exhibit distinct breeding seasons tracking food availability. If conspecific populations inhabit areas that experience different temporal cycles in food availability spurred by variation in precipitation regimes, then they should display asynchronous breeding seasons. Thus, such populations might exhibit a temporal barrier to gene flow, which may potentially promote genetic differentiation. We test a central prediction of this hypothesis, namely, that individuals living in areas with more asynchronous precipitation regimes should be more genetically differentiated than individuals living in areas with more similar precipitation regimes. Using mitochondrial DNA sequences, climatic data, and geographical/ecological distances between individuals of 57 New World bird species mostly from the tropics, we examined the effect of asynchronous precipitation (a proxy for asynchronous resource availability) on genetic differentiation. We found evidence for a positive and significant cross-species effect of precipitation asynchrony on genetic distance after accounting for geographical/ecological distances, suggesting that current climatic conditions may play a role in population differentiation. Spatial asynchrony in climate may thus drive evolutionary divergence in the absence of overt geographic barriers to gene flow; this mechanism contrasts with those invoked by most models of biotic diversification emphasizing physical or ecological changes to the landscape as drivers of divergence.

多数生物的繁殖季具有显著的季节性特征，且与食物资源的可获得性动态保持同步。若同种种群（conspecific populations）栖息于因降水格局（precipitation regimes）差异而导致食物可获得性时间动态不同的区域，则其繁殖季应当呈现异步性。因此，此类种群可能形成时间维度上的基因流（gene flow）障碍，进而有可能推动遗传分化（genetic differentiation）。我们对该假说的核心预测开展检验：即栖息于降水格局异步性更强区域的个体，其遗传分化程度应高于栖息于降水格局更为相似区域的个体。本研究依托线粒体DNA序列（mitochondrial DNA sequences）、气候数据，以及57种新世界鸟类（New World bird）（其中多数为热带类群）个体间的地理/生态距离，检验了异步降水（asynchronous precipitation，作为异步资源可获得性的替代指标）对遗传分化的影响。在控制地理/生态距离的影响后，我们发现降水异步性对遗传距离（genetic distance）存在跨物种的显著正向效应，这表明当前的气候条件可能在种群分化中发挥作用。由此可见，在不存在显性基因流地理障碍的情况下，气候空间异步性可能推动演化分化；这一机制与多数生物多样化（biotic diversification）模型所援引的驱动机制形成鲜明对比——后者多强调景观的物理或生态变化作为分化的驱动力。