Signal transmission and function in the complex displays of Puerto Rican Anolis lizards

Complexity is an important feature of signalling systems, with many organisms incorporating multiple signalling components into their communicative displays. However, why this complexity evolves remains poorly understood. One possible explanation is that different signal components optimize information transmission in different environmental contexts. We used models of signal attenuation to compare how information decays with distance across five distinct signal components in the complex visual displays of Puerto Rican Anolis lizards. We predicted that different signal components would differ in their suitability for short- versus long-distance communication. Consistent with this prediction, attenuation distances generally differed among signal components, suggesting that multicomponent displays may facilitate information transmission across different signalling contexts. Attenuation distance also varied considerably among species. To understand why, we examined how environmental factors influence interspecific variation in signal efficacy for each signal component. Specifically, we examined the effects of average receiver distance, ambient light and background visual noise on modelled signal performance across the 10 species of Anolis that occur on Puerto Rico. We found that species experiencing higher levels of visual noise exhibited greater attenuation distances for alert, headbob and dewlap movements, whereas species inhabiting brighter environments displayed alert and headbob signals that attenuated over shorter distances. In addition, species that display to receivers at greater distances showed greater attenuation distances for headbob displays. These results highlight how multiple environmental pressures interact to shape the design and functional performance of complex, multicomponent visual signals, and present a framework for exploring the ecological and evolutionary drivers of such signals across taxa.