Department of Integrative Biology, University of Windsor, Windsor, Ontario N9B 3P4, Canada.
Department of Psychology, Memorial University of Newfoundland, St John's, Newfoundland A1B 3X9, Canada.
Proc Biol Sci. 2021 Jan 13;288(1942):20202804. doi: 10.1098/rspb.2020.2804.
Closely related species often exhibit similarities in appearance and behaviour, yet when related species exist in sympatry, signals may diverge to enhance species recognition. Prior comparative studies provided mixed support for this hypothesis, but the relationship between sympatry and signal divergence is likely nonlinear. Constraints on signal diversity may limit signal divergence, especially when large numbers of species are sympatric. We tested the effect of sympatric overlap on plumage colour and song divergence in wood-warblers (Parulidae), a speciose group with diverse visual and vocal signals. We also tested how number of sympatric species influences signal divergence. Allopatric species pairs had overall greater plumage and song divergence compared to sympatric species pairs. However, among sympatric species pairs, plumage divergence positively related to the degree of sympatric overlap in males and females, while male song bandwidth and syllable rate divergence negatively related to sympatric overlap. In addition, as the number of species in sympatry increased, average signal divergence among sympatric species decreased, which is likely due to constraints on warbler perceptual space and signal diversity. Our findings reveal that sympatry influences signal evolution in warblers, though not always as predicted, and that number of sympatric species can limit sympatry's influence on signal evolution.
密切相关的物种通常在外观和行为上表现出相似性，但当相关物种在同域共存时，信号可能会发生分歧，以增强物种识别。先前的比较研究对这一假设提供了混合支持，但同域共存和信号分歧之间的关系可能是非线性的。信号多样性的限制可能会限制信号分歧，尤其是当大量物种同域共存时。我们测试了同域重叠对木莺（Parulidae）羽毛颜色和歌声分歧的影响，木莺是一个具有多样视觉和声音信号的物种丰富的群体。我们还测试了同域共存的物种数量如何影响信号分歧。与同域共存的物种对相比，异域共存的物种对总体上具有更大的羽毛和歌声分歧。然而，在同域共存的物种对中，雄性和雌性的同域重叠程度与羽毛分歧呈正相关，而雄性歌声带宽和音节率分歧与同域重叠呈负相关。此外，随着同域共存的物种数量增加，同域共存的物种之间的平均信号分歧减少，这可能是由于莺类感知空间和信号多样性的限制。我们的研究结果表明，同域共存会影响莺类的信号进化，但并不总是如预测的那样，同域共存的物种数量可以限制同域共存对信号进化的影响。
