Data from: Historical contingency and behavioural divergence in territorial Anolis lizards

The extent that evolution—including adaptation—is historically contingent (dependent on past events) has often been hotly debated, but is still poorly understood. In particular, there is little data on the degree that behaviour, an aspect of the phenotype that is strongly linked to contemporary environments (social or physical), retains the imprint of evolutionary history. In this study, I examined whether differences in the design of the territorial displays among species of Caribbean Anolis lizards reflect island specific selection regimes, or historically contingent predispositions associated with different clade histories. Adult males advertise territory ownership using a series of headbobs and dewlap extensions, bouts of which vary in duration among species. When display durations were mapped onto the Anolis phylogeny, prominent differences between species belonging to the Western and Eastern Caribbean radiations were apparent. Statistical analyses confirmed that species differences in the duration of headbob displays, and to some extent the duration of dewlap extensions, were historically contingent. The unique evolutionary histories of each clade have seemingly had a profound effect on the subsequent direction of display evolution among descendent taxa. These results combined with those from previous studies on these lizards show that past history can have an important impact on the type of behaviour exhibited by species today, to the point that adaptive evolution can proceed quite differently in lineages originating from different evolutionary starting points.

包括适应性演化（adaptive evolution）在内的演化过程在多大程度上具有历史偶然性（即依赖于过往事件），长期以来一直是学界激烈争论的议题，但目前仍未得到充分阐释。尤为关键的是，目前关于行为——作为与当代社会或物理环境紧密相关的表型（phenotype）特征——在多大程度上保留演化历史印记的相关数据仍十分匮乏。本研究旨在探究：加勒比安乐蜥（Anolis）各物种间领地展示行为模式的差异，究竟反映了岛屿特异性的选择机制，还是与不同支系（clade）演化历史相关的历史偶然性（historically contingent）演化倾向。成年雄性安乐蜥通过一系列头部俯仰动作与垂皮扩张动作来宣示领地所有权，不同物种间这些动作的持续时长存在差异。当将展示行为时长映射至安乐蜥系统发育树（phylogeny）时，属于加勒比西部与东部辐射演化（radiations）类群的物种间呈现出显著差异。统计分析结果证实：头部俯仰展示的时长以及垂皮扩张时长在一定程度上的物种间差异，确实具有历史偶然性。各个支系独特的演化历史，似乎对后续后代类群的展示行为演化方向产生了深远影响。结合此前针对该类蜥蜴的相关研究成果，本研究结果表明：过往演化历史对现代物种的行为模式具有重要影响，甚至可导致起源于不同演化起点的支系，其适应性演化路径呈现出显著差异。