Data from: Climate-driven build-up of temporal isolation within a recently formed avian hybrid zone

Divergence in the onset of reproduction can act as an important source of reproductive isolation (i.e. allochronic isolation) between co-occurring young species, but evidence for the evolutionary processes leading to such divergence is often indirect. While advancing spring seasons strongly affect the onset of reproduction in many taxa, it remains largely unexplored whether contemporary spring advancement directly affects allochronic isolation between young species. We examined how increasing spring temperatures affected onset of reproduction and thereby hybridization between pied and collared flycatchers (Ficedula spp.) across habitat types in a young secondary contact zone. We found that both species have advanced their timing of breeding in 14 years. However, selection on pied flycatchers to breed earlier was weaker, resulting in a slower response to advancing springs compared to collared flycatchers and thereby build-up of allochronic isolation between the species. We argue that a pre-adaptation to a broader niche use (diet) of pied flycatchers explains the slower response to raising spring temperature, but that reduced risk to hybridize may contribute to further divergence in the onset of breeding in the future. Our results show that minor differences in the response to environmental change of co-occurring closely related species can quickly cause allochronic isolation.

繁殖起始时间的分化，可作为同域分布的新生物种间生殖隔离的重要来源——这类隔离亦称异时隔离（allochronic isolation），但目前针对驱动此类分化的进化过程的相关证据，往往较为间接。尽管春季物候提前对多数类群的繁殖起始时间均具有显著影响，但当前的春季物候提前是否会直接影响新生物种间的异时隔离，目前仍未得到充分探索。本研究以一处新生的次生接触带中不同生境类型下的斑姬鹟（pied flycatchers）与领姬鹟（collared flycatchers，Ficedula spp.）为研究对象，探究春季气温升高如何影响二者的繁殖起始时间，进而影响其杂交进程。研究发现，在14年的观测周期内，两个物种的繁殖时间均有所提前。然而，斑姬鹟所承受的、促使其提前繁殖的自然选择压力较弱，相较于领姬鹟，其对春季物候提前的响应更为迟缓，进而导致两个物种间的异时隔离逐渐增强。本研究认为，斑姬鹟对更广生态位（食性）的预适应，可解释其对春季气温升高的响应更为迟缓的现象；而杂交风险的降低，或可在未来进一步推动二者繁殖起始时间的分化。本研究结果表明，同域分布的近缘物种对环境变化的响应存在细微差异，即可快速引发异时隔离。