Woodpecker drum evolution: an analysis of covariation in elements of a multicomponent acoustic display among and within species

Multicomponent signals are found throughout the animal kingdom, but how these elaborate displays evolve and diversify is still unclear. Here, we explore the evolution of the woodpecker drum display. Two components of this territorial, sexually selected signal, drum speed and drum length, are used by territory holders to assess the threat level of an intruding drummer. We explore the coevolution of these display components both among and within species. Among species, we find evidence for strong coevolution of drum speed and length. Within species, we find that drum speed and length vary largely independent of each other. However, in some species, there is evidence of covariation in certain portions of the drum length distribution. The observed differences in component covariation at the macro- and microevolutionary scales highlights the importance of studying signal structure both among and within species. In all cases of covariation at both evolutionary scales, the relationship between drum speed and length is positive, indicating mutual elaboration of display components, and not a performance trade-off.多组分信号广泛存在于动物界，但这类复杂的信号展示如何演化并产生多样性，目前仍未明晰。本研究聚焦于啄木鸟击鼓展示（woodpecker drum display）的演化过程。该受性选择调控的领地信号包含两个组分：击鼓速率与击鼓时长，领地持有者可通过这两个组分评估入侵击鼓者的威胁等级。我们对该信号组分在物种间与物种内的协同演化展开了探究。跨物种层面的分析显示，击鼓速率与击鼓时长存在显著的协同演化关系。物种内部层面，二者的变异整体呈现显著的相互独立性。但在部分物种中，击鼓时长分布的特定区间内，二者仍存在协变现象。宏演化与微演化尺度下信号组分协变模式的差异，凸显了同时开展跨物种与物种内信号结构研究的重要性。在两类演化尺度下的所有协变案例中，击鼓速率与击鼓时长均呈正相关关系，这表明信号组分是协同强化而非存在性能权衡。