Testing the factors on the evolution of movement-based visual signal complexity in an Asian agamid lizard

Abstract

Elucidating the factors that influence the evolution of signal complexity is essential in understanding animal communication. Compared to vocal and color signals, movement-based visual signals only start to attract attention recently. In this study, we tested the social complexity (social structure promotes signal complexity) and background noise hypotheses (background noise promotes signal complexity) on the evolution of movement-based visual signal complexity. We collected display signals from twelve populations across the distribution range of the Asian agamid lizard, Phrynocephalus przewalskii. Their various components (tail coil, tail lash, body turning, and limb flapping) were quantified. Furthermore, we measured the population density and sexual size dimorphism (SSD), as estimates of social complexity, and estimate background noise using presence of plant and wind speed. We tested associations between measurements of variability in individual signal components and the overall display with estimates of social complexity and background noise using linear mixed models. We found evidence to suggest that both SSD and the noise environment impact the delivery of multiple display components, particularly the duration and maximum speed of display components. Importantly, our findings suggest that social and environmental factors do not impact males and females equally. Our data are consistent with both social complexity and background noise hypotheses, and our research provides direct evidence on the links among display complexity, social complexity, and background noise.

Significance statement

The evolution of animal signal complexity has fascinated biologists for generations. We know much about vocal and color signals; nevertheless, movement-based visual signals only start to attract attention recently. Here we tested the factors influencing the evolution of display complexity using P. przewalskii as a study system, particularly around the social complexity (social structure promotes signal complexity) and background noise hypotheses (background noise promotes signal complexity). Our data are consistent with both social complexity and background noise hypotheses and provide direct evidence on the links among movement-based visual signal complexity, social complexity, and background noise.