Information content is more important than sensory system or physical distance in guiding the long-term evolutionary relationships between signaling modalities in Sceloporus lizards

Long-term signal evolution is shaped by a variety of selective pressures including the need to convey additional information or to improve message transfer to specific receivers or through multiple environments. Here, we test the relative importance of information and sensory modality in shaping the long-term evolution of multimodal signals in Sceloporus lizards. To broadcast identity at territorial boundaries, male Sceloporus use both visual motion (headbob) and chemical signals, whereas they use color (blue belly patches) to signal aggression. Using modern phylogenetic comparative methods, we found a negative correlation between evolutionary changes in visual motion (headbobs) and chemical (femoral pore) signals, but only indirect ties between the evolution of color and motion signals (both of which are perceived visually) through viviparity, and no evidence of an evolutionary link between color and chemical signals. We also find a negative correlation between arboreality and chemical signals. Thus, information content (in this case, broadcasting individual identity versus signaling aggression) appears to play a more important role than sensory modality or physical distance in guiding long-term signal evolution. Additional insights into the underlying evolutionary processes are described, illustrating the utility of a phylogenetic approach.

长期信号演化受多种选择压力塑造，包括传递额外信息、优化向特定接收者或跨多环境的信息传递等需求。本研究以侧褶蜥属（Sceloporus）蜥蜴的多模态信号（multimodal signals）长期演化为研究对象，检验信息与感觉模态（sensory modality）对其演化的相对重要性。为在领地边界处传递个体身份信息，雄性侧褶蜥同时使用视觉运动信号——点头动作（headbob）与化学信号；而它们则通过体色——蓝色腹斑（blue belly patches）传递攻击性信号。本研究采用现代系统发育比较方法（phylogenetic comparative methods）开展分析，结果显示：视觉运动信号（点头动作headbobs）与化学信号（股孔femoral pore）的演化变化呈负相关；但体色信号与视觉运动信号（二者均为视觉感知信号）的演化仅通过胎生（viviparity）存在间接关联，未发现体色信号与化学信号之间存在演化联系的证据。此外，本研究还发现树栖性（arboreality）与化学信号呈负相关。综上，信息内容（本研究中即传递个体身份与传递攻击性信号的差异）在指导长期信号演化方面，相较感觉模态或物理距离发挥了更为关键的作用。本研究还对背后的潜在演化过程提供了额外见解，印证了系统发育研究方法的应用价值。