Data from: Testing alternative hypotheses for evolutionary diversification in an African songbird: rainforest refugia versus ecological gradients

Geographic isolation in rainforest refugia and local adaptation to ecological gradients may both be important drivers of evolutionary diversification. However, their relative importance and the underlying mechanisms of these processes remain poorly understood because few empirical studies address both putative processes in a single system. A key question is to what extent is divergence in signals that are important in mate and species recognition driven by isolation in rainforest refugia or by divergent selection across ecological gradients? We studied the little greenbul, Andropadus virens, an African songbird, in Cameroon and Uganda, to determine whether refugial isolation or ecological gradients better explain existing song variation. We then tested whether song variation attributable to refugial or ecological divergence was biologically meaningful using reciprocal playback experiments to territorial males. We found that much of the existing song variation can be explained by both geographic isolation and ecological gradients, but that divergence across the gradient, and not geographic isolation, affects male response levels. These data suggest that ecologically divergent traits, independent of historical isolation during glacial cycles, can promote reproductive isolation. Our study provides further support for the importance of ecology in explaining patterns of evolutionary diversification in ecologically diverse regions of the planet.

雨林避难所（rainforest refugia）中的地理隔离与沿生态梯度的局部适应，均可能为演化分化（evolutionary diversification）的重要驱动因子。然而，二者的相对重要性及内在作用机制仍不甚明晰，目前鲜有实证研究能在同一研究系统中同时探究这两类假定过程。一个核心科学问题为：在配偶与物种识别（mate and species recognition）中发挥关键作用的信号分化，在多大程度上由雨林避难所的地理隔离驱动，又或是由沿生态梯度的歧化选择（divergent selection）塑造？我们以分布于喀麦隆与乌干达的非洲鸣禽小绿鹎（Andropadus virens）为研究对象，旨在明确避难所隔离与生态梯度二者中，何者能更好地解释现存的鸣唱变异。随后，我们通过针对领域雄鸟的互惠回放实验（reciprocal playback experiments），检验了归因于避难所隔离或生态分化的鸣唱变异是否具备生物学意义。研究结果显示，现存的大部分鸣唱变异可由地理隔离与生态梯度共同解释，但仅沿梯度的歧化分化（而非地理隔离）会影响雄鸟的响应水平。本研究数据表明，独立于冰期周期内历史隔离事件的生态分化性状，可推动生殖隔离（reproductive isolation）的形成。本研究进一步支持了生态过程在解释地球生态多样区域演化分化格局中的重要性。