Data from: Shaping communicative color signals over evolutionary time

Many evolutionary forces can shape the evolution of communicative signals, and the long-term impact of each force may depend on relative timing and magnitude. We use a phylogenetic analysis to infer the history of blue belly patches of Sceloporus lizards, and a detailed spectrophotometric analysis of four species to explore the specific forces shaping evolutionary change. We find that the ancestor of Sceloporus had blue patches. We then focus on four species; the first evolutionary shift (captured by comparison of S. merriami and S. siniferus) represents an ancient loss of the belly patch by S. siniferus, and the second evolutionary shift, bounded by S. undulatus and S. virgatus, represents a more recent loss of blue belly patch by S. virgatus. Conspicuousness measurements suggest that the species with the recent loss (S. virgatus) is the least conspicuous. Results for two other species (S. siniferus and S. merriami) suggest that over longer periods of evolutionary time, new signal colors have arisen which minimize absolute contrast with the habitat while maximizing conspicuousness to a lizard receiver. Specifically, males of the species representing an ancient loss of blue patch (S. siniferus) are more conspicuous than are females in the UV, whereas S. merriami males have evolved a green element that makes their belly patches highly sexually-dimorphic but no more conspicuous than the white bellies of S. merriami females. Thus, our results suggest that natural selection may act more immediately to reduce conspicuousness, while sexual selection may have a more complex impact on communicative signals through the introduction of new colors.

诸多演化动力（evolutionary forces）均可塑造通讯信号（communicative signals）的演化进程，而每种动力的长期影响，往往取决于其作用的相对时序与强度。本研究通过系统发育分析（phylogenetic analysis）推断棘蜥属（Sceloporus）蜥蜴腹部蓝色斑块的演化历史，并对4个物种开展细致的分光光度分析（spectrophotometric analysis），以探究驱动演化改变的具体动力。研究结果显示，棘蜥属的祖先类群已演化出腹部蓝色斑块。随后本研究聚焦于4个物种：第一个演化转变（通过对比梅氏棘蜥（S. merriami）与西氏棘蜥（S. siniferus）得以揭示）对应西氏棘蜥古老的腹部蓝色斑块丢失事件；第二个演化转变（以波氏棘蜥（S. undulatus）与维氏棘蜥（S. virgatus）为分界）则代表维氏棘蜥较晚近的腹部蓝色斑块丢失事件。醒目度检测结果显示，发生较晚近斑块丢失的维氏棘蜥，其醒目程度最低。另外两个物种（西氏棘蜥与梅氏棘蜥）的研究结果表明，在更长的演化时间尺度下，新的通讯信号色彩得以演化：这类色彩在最大化蜥蜴接收者可辨识性的同时，尽可能降低了与栖息环境的绝对对比度。具体而言，发生古老蓝色斑块丢失的西氏棘蜥，其雄性个体在紫外（UV）波段的醒目程度高于雌性；而梅氏棘蜥的雄性则演化出绿色色彩元素，使其腹部斑块呈现出高度的性二态性，但其醒目程度并未超过梅氏棘蜥雌性的白色腹部。综上，本研究结果表明：自然选择（natural selection）可能更直接地作用于降低信号的醒目程度，而性选择（sexual selection）则通过引入新的色彩，对通讯信号产生更为复杂的影响。