The effect of turbidity on female mate choice in the guppy

Animals often moderate behaviours based on environmental and social cues to enhance their chances of survival and reproductive success. This requires reliable cues that reflect changes in ambient conditions. Environmental pollutants can increase communication costs and distort the accuracy of received information, leading to negative effects on the outcome of behavioural adjustments. Consequently, selection may reduce behavioural plasticity to avoid errors or promote more prudent decision-making when certain cues become unreliable. In aquatic ecosystems, water turbidity shows high levels of natural variation, but human activities amplify its magnitude and extent by increasing algae and suspended solids in the water. Here, we investigated how elevated levels of water turbidity affected mating decisions made by female guppies (Poecilia reticulata) in a laboratory setting. Guppies are a widespread species with a broad tolerance of polluted environments, and females rely heavily on visual cues when making mate choice decisions. We manipulated turbidity by adding suspended solids to water and tested how this affected female preference for males with more orange coloration. We found that females spent more time near males with a greater area of orange colouration in low turbidity water, but that this preference disappeared in both the mid and high turbid water treatments. Moreover, female preferences were highly repeatable in low turbidity water and high turbidity water but not in mid turbidity water. Together, our results suggest that water turbidity impairs the ability of females to discern male colouration and affects the consistency of mate preferences. This could have consequences for the evolution of male colouration in turbid waters.