Shaping communicative colour signals over evolutionary time.

Alison G Ossip-Drahos,Diana K Hews,Emília P Martins,J Jaime Zúñiga-Vega,Cuauhcihuatl Vital-García,José R Oyola Morales

doi:10.1098/rsos.160728

Abstract

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 colours 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, whereas sexual selection may have a more complex impact on communicative signals through the introduction of new colours.

Highlights

Communicative signals are shaped by a complex combination of evolutionary forces that can shift over time, and we can use comparative studies to explore how and when signals respond to different evolutionary forces [1,2,3,4]
Our results are consistent with the hypothesis that the blue belly patches of male Sceloporus lizards have been lost repeatedly
The bellies of S. virgatus males, a species that has lost the blue patch relatively recently, closely resemble the habitat in which they are found, suggesting that natural selection may be responsible for the loss and is capable of having a very fast impact, making these lizards less conspicuous to predators or other unwanted receivers

Summary

Introduction

Communicative signals are shaped by a complex combination of evolutionary forces that can shift over time, and we can use comparative studies to explore how and when signals respond to different evolutionary forces [1,2,3,4]. Natural and sexual selection act on different elements of the signal. Dorsal colours are often shaped by natural selection to make an animal cryptic to predators, whereas the impact of sexual selection is focused on signalling colours that are dramatically displayed only to conspecifics [5,6]. Natural and sexual selection act differentially on senders and receivers or at different points in time. The sensory bias hypothesis predicts that natural selection first impacts receiver sensory systems, and is followed by sexual selection acting on signal production (reviewed in [7]). We use phylogenetic analyses and reflectance spectrometry measurements of four representative Sceloporus lizard species to explore changes in a communicative signal over long periods of evolutionary time

Methods

Results

Conclusion