Acoustic signal perception in a noisy habitat: lessons from synchronising insects

Abstract

Acoustically communicating animals often have to cope with ambient noise that has the potential to interfere with the perception of conspecific signals. Here we use the synchronous display of mating signals in males of the tropical katydid Mecopoda elongata in order to assess the influence of nocturnal rainforest noise on signal perception. Loud background noise may disturb chorus synchrony either by masking the signals of males or by interaction of noisy events with the song oscillator. Phase-locked synchrony of males was studied under various signal-to-noise ratios (SNRs) using either native noise or the audio component of noise (<9 kHz). Synchronous entrainment was lost at a SNR of −3 dB when native noise was used, whereas with the audio component still 50 % of chirp periods matched the pacer period at a SNR of −7 dB. Since the chirp period of solo singing males remained almost unaffected by noise, our results suggest that masking interference limits chorus synchrony by rendering conspecific signals ambiguous. Further, entrainment with periodic artificial signals indicates that synchrony is achieved by ignoring heterospecific signals and attending to a conspecific signal period. Additionally, the encoding of conspecific chirps was studied in an auditory neuron under the same background noise regimes.

Competition and cooperation in a synchronous bushcricket chorus

“…We simulated the active space of synchronous signallers by means of a two-dimensional multi-agent computer model that was developed in Netlogo (v. 5.0). Simulations of the active space are based on realistic sound propagation properties observed in the field [ 35 ] and take into account the hearing threshold of receivers, which was set to either 40 or 50 dB SPL, whereby a hearing threshold of 40 dB SPL roughly corresponds to silent laboratory conditions [ 38 , 39 ]. Mecopoda choruses have been recorded in the field exclusively in rainforest clearings where variation in the third dimension was small (M. Hartbauer 2012, personal observation).…”

The importance of invertebrates when considering the impacts of anthropogenic noise

“…Römer et al [38] found modifications to the temporal calling patterns in two sympatric katydid species, Hemisaga dendiculata and Mygalopsis marki, that almost completely overlap in call frequency, with H. dendiculata song suppressed in the presence of calling M. marki. In another species, Mecopoda elongata, which sings in choruses, levels of synchrony were reduced with increasing nocturnal rainforest noise [39]. Background noise can also induce changes in phonotaxis (the ability to move in an orientation with respect to a sound source).…”

Genomics: moving behavioural ecology beyond the phenotypic gambit

“…Indeed recent studies suggest that the concept can be applied to complex behavioural phenotypes, for example sociality, which is multifaceted and has several phylogenetic origins (Fischman, Woodard, & Robinson, 2011; Toth & Robinson, 2009; Toth et al, 2007). Behavioural ecologists have uncovered a surprising diversity of complex phenotypes that have arisen repeatedly across taxa, for example, reproductive strategies like male chorusing and female-mimicking male sneaking behaviours, and foraging behaviours like echolocation (Hanlon, Naud, Shaw, & Havenhand, 2005; Hartbauer, Siegert, Fertschai, & Romer, 2012; Jordão, Fonseca, Amorim, & Janik, 2012; Parker et al, 2013; Taborsky, 2008). A genomic approach could begin to address whether shared mechanisms, in addition to ecological factors, are in part responsible for this type of convergence (Arendt & Reznick, 2008).…”