Abstract
Optimal mate choice based on the assessment of communication signals can be constrained by multiple sources of noise. One well-known impediment to acoustically guided mating decisions is the ambient noise created by multiple signaling individuals in large social groups, in which ambient noise can mask signals by impairing signal recognition and discrimination by receivers. Although studied far less often, another potential source of noise in communication systems stems from variability or inconsistency in how signalers produce their signals. Consistency is especially important in the context of mate choice because sexual advertisement signals are frequently produced repeatedly through time and are composed of constituent parts (e.g., notes, pulses) that are repeated within signals. Inconsistent signal production within individuals has the potential to mask between-individual differences that are often the target of receiver decision-making. In this study of Cope’s gray treefrog, Hyla chrysoscelis, we tested the hypothesis that ambient noise and inconsistent signaling, both independently and synergistically, impair discrimination of species identity. We assayed female discrimination based on pulse rate, a signal of species identity, in quiet and at three levels of ambient noise designed to simulate a breeding chorus. We used synthetic advertisement calls that were invariant or generated with one of three experimental levels of inconsistency in pulse rate, chosen based on levels of within-individual variation observed in natural calls. Pulse rate discrimination was impaired by average and above-average levels of chorus noise, but not by inconsistency in signal production. Receivers spent slightly more time making decisions at the highest level of chorus noise, but response latencies were unaffected by inconsistency. There was no evidence of synergism between ambient noise and inconsistency. Our results suggest that ambient noise, but not inconsistency in signal production, may limit sexual selection on a signal of species identity in natural settings.
Highlights
While the impacts of biotic, abiotic, and anthropogenic sources of ambient noise are increasingly recognized (Römer, 2013; Reichert and Ronacher, 2015; Wiley, 2015; Slabbekoorn et al, 2018; Dominoni et al, 2020), other potential sources of noise in animal communication are rarely explored
We recently showed that both ambient chorus noise and inconsistent signaling impair the ability of female H. chrysoscelis to discriminate among potential mates based on differences in their rate of call production (“call rate”) (Tanner and Bee, 2020), a potential non-arbitrary signal of male quality due to the high metabolic cost of signaling (Taigen and Wells, 1985)
We investigated the effects of ambient chorus noise and inconsistent signaling on the ability of female H. chrysoscelis to discriminate among potential mates based on a signal of species identity
Summary
While the impacts of biotic, abiotic, and anthropogenic sources of ambient noise are increasingly recognized (Römer, 2013; Reichert and Ronacher, 2015; Wiley, 2015; Slabbekoorn et al, 2018; Dominoni et al, 2020), other potential sources of noise in animal communication are rarely explored. Previous studies of H. chrysoscelis have measured the extent of within-individual variation in pulse rates (Ward et al, 2013b) and established that inconsistency does not signal body condition or size (Tanner and Bee, 2019) and potentially acts as a source of noise in the communication channel in that it could obscure receiver estimates of meaningful call characteristics. We further predicted that response latencies would increase in noisy conditions and when subjects discriminated between highly inconsistent and more similar pulse rates because, in these difficult discrimination tasks, subjects might benefit from increased assessment times
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