Staying tuned: grasshoppers from noisy roadside habitats produce courtship signals with elevated frequency components

Abstract

Summary1. Anthropogenic noise is known to affect acoustic signal production in birds, frogs and mammals. These animals use different mechanisms to adjust their signals to elevated background noise levels (increase in signal amplitude, shift to higher frequencies, etc.). Previous studies have concentrated on behaviourally plastic changes in signal production as a result of elevated background noise levels. To our knowledge, long-term effects of anthropogenic noise on signal production have not yet been investigated. Moreover, strategies of invertebrate species to ensure acoustic signal transmission under anthropogenic noise have not been examined, so far. 2. We tested whether and how male Chorthippus biguttulus grasshoppers from noisy roadside habitats may adjust acoustic courtship signals to elevated background noise levels, compared with conspecifics from quiet control habitats. In this species, sexually selected male courtship signals serve to attract potential mating partners, which make the undisturbed transmission of signals in habitats with increased background noise levels crucial for male reproductive success. 3. Compared to males from control populations, males from roadside habitats produced songs with a significantly higher local frequency maximum under standardized, quiet recording conditions. This local frequency maximum (in the range of c. 6-9 kHz) overlaps with low-frequent road noise that has the potential to degrade or mask this part of the signals' frequency spectrum. 4. To our knowledge, this is the first evidence that insects from noisy habitats produce different acoustic signals than conspecifics from quiet habitats, possibly using a more permanent mechanism for signal adjustment than behavioural plasticity, which was found in different bird species adjusting to high background noise levels. Such an effect of anthropogenic noise has not been shown for any invertebrate species before, and our results suggest that similar strategies to avoid degradation or masking by noise (i.e. increase in carrier frequency) are used over a wide range of taxa, including both, vertebrates and invertebrates.

Genome size variation affects song attractiveness in grasshoppers: Evidence for sexual selection against large genomes

“…Subjects were transferred to the laboratory and recorded using a Bruel & Kjaer 4939 microphone (Naerum, Denmark) in combination with an UltraSoundGate 116 recording system (Avisoft Bioacoustics, Berlin, Germany) and processed by Avisoft-SASLab Pro bioacoustics software 4.3 (Avisoft Bioacoustics, Berlin, Germany; see Lampe et al 2012 for details on the recording setup). We analyzed three songs per individual.…”

The importance of invertebrates when considering the impacts of anthropogenic noise

“…Shieh et al [12] compared the calling behaviour of the cicada Cryptotympana takasagona in noisy and quiet urban parks, finding positive correlations between noise levels and both call frequency and chorusing. Lampe et al [13] found that male bow-winged grasshoppers (Chorthippus biguttulus) collected from noisy roadsides sang with a greater low-frequency component than males collected from paired quiet areas nearby. As male singing was recorded in the absence of noise stimuli in anechoic chambers, the differences are unlikely to be the consequence of behavioural plasticity, but instead may result from longer term adaptation.…”

Decision making and preferences for acoustic signals in choice situations by female crickets

“…Therefore, the quality of a given signal is not necessarily positively correlated with intensity. In addition, further sound sources such as abiotic (Brumm and Slabbekoorn, 2005;Reichert and Ronacher, 2015) or even anthropogenic noise (Lampe et al, 2012(Lampe et al, , 2014Schmidt et al, 2014) may impede signal representation and recognition. Crickets, bushcrickets and grasshoppers are known to employ several processing tools to reduce the detrimental effects of masking and noise (Einhäupl et al, 2011;Schmidt and Römer, 2011;Neuhofer and Ronacher, 2012;Hildebrandt et al, 2015), most prominently by forward masking, selective attention, formation of acoustic hemispheres and stream segregation (Pollack, 1986;Schul and Sheridan, 2006;Triblehorn and Schul, 2009;Schmidt and Römer, 2011).…”