Abstract
In response to anthropogenic noise, vertebrates express modified acoustic communication signals either through individual plasticity or local population adaptation. In contrast, how insects respond to this stressor is poorly studied. Field crickets Gryllus bimaculatus use acoustic signals to attract and locate mates and are commonly found in noisy roadside environments, offering a powerful system to study the effects of anthropogenic noise on insect communication. Rapid repetition of sexual calls (chirps) is essential to attract females, but calling incurs energetic costs and attracts predators. As a result, males are predicted to reduce calling rates when background noise is high. Here, we combine observations and experimental playbacks to show that the responses of field cricket males to anthropogenic noise also depend on their previous experience with passing cars. First, we show that males living on highway edges decrease their chirp rate in response to passing cars. To assess whether this behavioral response depends on previous exposure to car noise, we then broadcast recordings of car noise to males located at different distances from the road and, therefore, with different previous exposure to car noise. Although all tested individuals responded to broadcasted traffic noise, males closest to the road decreased their chirp rate less than individuals calling further from the road. These results suggest that regular exposure to anthropogenic noise may decrease individuals’ sensitivity and behavioral responses to noise, allowing them to maintain effective signaling rates. Behavioral plasticity modulated by experience may thus allow some insect species to cope with human-induced environmental stressors.
Highlights
Signaling in noisy environments can reduce perception by intended receivers, leading animals to flexibly adapt their signals in response to natural variation in noise
Our results demonstrate that field cricket G. bimaculatus males adjust their singing behavior to match the current level of ambient noise; they rapidly decrease their chirp rate in response to louder traffic noise
We studied a population of individuals continuously distributed, making it likely that there is significant exchange of genes between individuals breeding close to and far from roads, which is likely to erode local adaptation over such short spatial scales
Summary
Signaling in noisy environments can reduce perception by intended receivers, leading animals to flexibly adapt their signals in response to natural variation in noise. Anthropogenic noise is often loudest at low frequencies, and individuals from some anurans, insects, and songbird species shift the signal band upwards to avoid masking (Slabbekoorn and Peet 2003; Parris et al 2009; Lampe et al 2012; Potvin and Mulder 2013; Slabbekoorn 2013; but see Brumm and Bee 2016; Brumm 2017) Another strategy to improve the signal-to-noise ratio consists of increasing the signal amplitude, the Lombard effect (Lombard 1911), which has been demonstrated in, for example, male “nightingales, Luscinia megarhynchos” (Brumm 2004). Given that human-made noise varies both spatially and temporally, an important distinction is the degree to which responses to noise are influenced by previous exposure, either on the individual or population level
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