Noise pollution and artificial light at night alter selection pressures on sexual signals in an urban adapter

Human-induced environmental changes can have major impacts on how individuals communicate. Species using sexual signals may experience especially rapid shifts in their interactions with both intended receivers (mates) and eavesdroppers (predators). Artificial light at night and anthropogenic noise represent 2 major environmental features of human-dominated habitats which may alter selection pressures imposed on sexual signalers. In this study, we used a full factorial design to investigate individual and combined effects of experimentally added light and noise pollution on the attraction of female frogs and bat predators to speakers broadcasting male túngara frog (Engystomops pustulosus) calls. We conducted 2-choice tests in the field to examine whether predatory and mating preferences for signals differing in conspicuousness change in response to noise and light pollution. Light pollution reduced the number of approaches from predators and mates attracted to our playbacks. The addition of noise pollution enhanced this effect on predators but decreased it for female frogs. Light also lowered female frog preference for conspicuous calls, but this effect was counteracted when noise pollution was added. Reduced numbers of predators and female frogs found under lit conditions suggest light pollution can both reduce natural selection and increase sexual selection pressures on male signals. These findings indicate that light pollution could be responsible for the reduced numbers of predatory bats and female frogs found in urban environments, providing a causal explanation for more conspicuous and attractive sexual signalling in males from urban populations.