Data from: Reproductive character displacement of female, but not male song discrimination in an avian hybrid zone

Divergence of male sexual signals and female preferences for those signals often maintains reproductive boundaries between closely related, co-occurring species. However, contrasting sources of selection, such as interspecific competition, can lead to weak divergence or even convergence of sexual signals in sympatry. When signals converge, assortative mating can be maintained if the mating preferences of females diverge in sympatry (reproductive character displacement; RCD), but there are few explicit examples. Pied flycatchers (Ficedula hypoleuca) are sympatric with collared flycatchers (F. albicollis) on the Baltic island of Öland, where males from both species compete over nestboxes, their songs converge, and the two species occasionally hybridize. We compare song discrimination of male and female pied flycatchers on Öland and in an allopatric population on the Swedish mainland. Using field choice trials, we show that male pied flycatchers respond similarly to the songs of both species in sympatry and in allopatry, while female pied flycatchers express stronger discrimination against heterospecific songs in sympatry than in allopatry. These results are consistent with RCD of song discrimination of female pied flycatchers where they co-occur with collared flycatchers, which should maintain species assortative mating despite convergence of male sexual signals.雄性性信号与雌性对该信号的偏好的分化，通常维持着近缘同域分布物种间的生殖隔离界限。然而，种间竞争这类对立的选择压力，可能导致同域物种的性信号分化减弱甚至趋同。当性信号发生趋同时，若雌性的交配偏好于同域环境下发生分化（即生殖特征置换，Reproductive Character Displacement，RCD），仍可维持选型交配（assortative mating），但此类明确的实证案例较为匮乏。斑姬鹟（*Ficedula hypoleuca*）与领姬鹟（*F. albicollis*）在波罗的海的厄兰岛同域分布，二者雄性会竞争巢箱，鸣唱信号趋于一致，且二者偶有杂交发生。我们分别对厄兰岛同域种群与瑞典本土的异域种群的斑姬鹟雌雄个体的鸣唱识别能力进行了比较。借助野外选择实验（field choice trials），我们发现：无论处于同域还是异域环境中，雄性斑姬鹟对两种物种的鸣唱反应均无显著差异；而雌性斑姬鹟在同域环境中对异种鸣唱的识别能力，显著强于异域种群中的雌性个体。上述结果与雌性斑姬鹟在与领姬鹟同域分布时发生鸣唱识别的生殖特征置换相符，该机制可在雄性性信号趋同的背景下，维持物种间的选型交配。