Light modulates population differences in alternative mating tactics in Trinidadian guppies

Abstract

A major goal in evolutionary biology is to understand how trade-offs between natural and sexual selection drive the evolution and maintenance of secondary sexual traits. Many organisms exhibit bright, conspicuous colour signals to attract mates, but these signals often come at the cost of increased predation. One way to reduce predation risk is to adjust behaviour according to circadian changes in the local light environment because light determines the perceived conspicuousness of a visual signal. In this study we consider how male mating behaviours change throughout the day in two groups of Trinidadian guppies, Poecilia reticulata, adapted to different levels of predation risk. Using outdoor stream mesocosms, we found that fish adapted to higher predation risk reduced their conspicuous courtship display during midday high-light conditions but increased courtship in the morning and evening conditions. In contrast, low-predation guppies courted in the morning but not in the evening. Males from both habitats reduced courtship when it was brighter, but high-predation males were more sensitive to brightness and hue variations in the morning and evening hours. These results highlight the importance of light environment on courtship display strategies and its consequences on the evolution of sexually selected traits.