Within-individual variation in signal production limits female choice in noisy treefrog choruses

Abstract

In acoustically communicating animals such as anurans and orthopterans, individual signalers can display remarkable variation in signal traits, even within a single bout of calling. This within-individual variation has the potential to “mask” the between-individual variation that is the target of sexual selection. Thus, receivers may not always be able to discriminate among males based on properties of their acoustic signals, even when female choice is well documented in the lab. The effect of within-individual variation may be compounded by noise generated by breeding choruses of conspecifics, which can prevent signal detection or discrimination. We manipulated within-individual variation in two signal traits (call rate and pulse rate) that are critically important for mate choice in Hyla chrysoscelis, Cope’s gray treefrog. We replicated our design at three realistic levels of chorus noise. Within-individual variation in signal traits reduced the strength of sexual selection on one of two traits, and receivers were less likely to discriminate against lower-quality signals under conditions of realistic chorus noise. Our results suggest that preference functions generated using stimuli that lack within-individual variation, under ideal listening conditions, may chronically over-estimate the strength of sexual selection on signal traits in natural populations.