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.

中文翻译：

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Sympatry 驱动木莺 (Parulidae) 的颜色和歌曲进化

密切相关的物种通常在外观和行为上表现出相似性，但是当相关物种存在于同源中时，信号可能会发散以增强物种识别。先前的比较研究为这一假设提供了不同的支持，但同源性和信号发散之间的关系可能是非线性的。对信号多样性的限制可能会限制信号的分歧，特别是当大量物种是同域的时。我们测试了同域重叠对木莺 (Parulidae) 羽毛颜色和歌曲分歧的影响，这是一个具有不同视觉和声音信号的特殊群体。我们还测试了同域物种的数量如何影响信号分歧。与同域物种对相比，异域物种对具有更大的羽毛和歌曲差异。然而，在同域物种对中，羽毛分歧与雄性和雌性的同域重叠程度呈正相关，而雄性歌曲带宽和音节率分歧与同域重叠呈负相关。此外，随着同域物种数量的增加，同域物种之间的平均信号差异减少，这可能是由于莺感知空间和信号多样性的限制。我们的研究结果表明，sympatry 会影响莺的信号进化，尽管并不总是如预期的那样，并且 sympatric 物种的数量可以限制 sympatry 对信号进化的影响。同域物种之间的平均信号差异减少，这可能是由于莺感知空间和信号多样性的限制。我们的研究结果表明，sympatry 会影响莺的信号进化，尽管并不总是如预期的那样，并且 sympatric 物种的数量可以限制 sympatry 对信号进化的影响。同域物种之间的平均信号差异减少，这可能是由于莺感知空间和信号多样性的限制。我们的研究结果表明，sympatry 会影响莺的信号进化，尽管并不总是如预期的那样，并且 sympatric 物种的数量可以限制 sympatry 对信号进化的影响。