R Code file from Evolutionary loss of a signalling colour is linked to increased response to conspecific chemicals

Behavioural responses to communicative signals combine input from multiple sensory modalities and signal compensation theory predicts that evolutionary shifts in one sensory modality could impact response to signals in other sensory modalities. Here, we conducted two types of field experiments with 11 species spread across the lizard genus <i>Sceloporus</i> to test the hypothesis that the loss of visual signal elements affects behavioural responses to a chemical signal (conspecific scents) or to a predominantly visual signal (a conspecific lizard), both of which are used in intraspecific communication. We found that three species that have independently lost a visual signal trait, a colourful belly patch, responded to conspecific scents with increased chemosensory behaviour compared to a chemical control, while species with the belly patch did not. However, most species, with and without the belly patch, responded to live conspecifics with increased visual displays of similar magnitude. While aggressive responses to visual stimuli are taxonomically widespread in <i>Sceloporus</i>, our results suggest that increased chemosensory response behaviour is linked to colour patch loss. Thus, interactions across sensory modalities could constrain the evolution of complex signalling phenotypes, thereby influencing signal diversity.

针对通讯信号的行为响应整合了多感官模态的输入信息，而信号补偿理论预测，某一感官模态的演化转变可能会影响其他感官模态下的信号响应。本研究针对分布于侧斑鬣蜥属（Sceloporus）的11个物种开展了两类野外实验，以检验如下假说：视觉信号元件的缺失会影响动物对化学信号（同种个体气味）或以视觉为主的信号（同种蜥蜴）的行为响应——这两类信号均用于种内通讯。我们发现，三个独立丢失了视觉信号特征（彩色腹部斑块）的物种，相较于化学对照组，其对同种气味的化学感应行为显著增强，而保留腹部斑块的物种则无此现象。不过，无论是否带有腹部斑块，大多数物种对活体同种个体的视觉展示行为均有显著提升，且提升幅度相近。尽管针对视觉刺激的攻击响应在侧斑鬣蜥属中具有广泛的分类学分布，但本研究结果表明，化学感应响应行为的增强与腹部斑块的丢失存在关联。综上，跨感官模态的相互作用可能会约束复杂信号表型的演化，进而影响信号多样性。