High-frequency sound transmission in natural habitats: implications for the evolution of insect acoustic communication

Abstract

Transmission and reception of high-frequency sound in the natural environment of bushcrickets (Tettigonia viridissirna L.) was studied using the activity of an identified neuron in the insect's auditory pathway as a "biological microphone". Different positions of the receiver within the habitat were simulated by systematic variation of the distance from a loudspeaker and the height above the ground. Attenuation and filtering properties of the habitat were investigated with pure-tone frequencies between 5 and 40 kHz. Sound attenuation in excess of the attenuation due to geometrical spreading alone increased with increasing frequency, distance between sender and receiver, and decreasing height within the vegetation (Figs. 2-4). The data also confirm the existence of two kinds of excess attenuation. The amount of amplitude fluctuations in the sound signals was investigated by analysing the variability of the neuronal responses at a given receiver position. Variability increased with decreasing bandwidth of a noise signal at some distance from the loadspeaker. The variability in the responses to pure tones increased with both increasing frequency and distance from the source (Fig. 7). In the selected habitat, the temporal pattern of the natural calling song of male T. viridissima was very reliably reflected in the activity of the recorded neuron up to a distance of 30 m at the top of the vegetation, and 15-20 m near ground level (Figs. 5, 8). The maximum hearing distance in response to the calling song was about 40 m. Environmental constraints on long-range acoustic communication in the habitat are discussed in relation to possible adaptations of both the signal structure and the behavior of the insects.

Neural Mechanisms for Acoustic Signal Detection under Strong Masking in an Insect

“…6), we would expect a breakdown of selectivity when the 2 kHz component falls below threshold at higher sender-receiver distances. However, in the natural habitat low frequencies suffer much less from excess attenuation compared with higher frequencies (Romer and Lewald, 1992). It is thus likely that at higher communication distances the 2 kHz component can still activate LFRs, due to the low-frequency advantage in sound transmission, although their absolute sensitivity is reduced compared with HFRs.…”

“…Because of the reduced sampling rate of the Edirol A/D audio interface, the signal playback resulted in a strong attenuation of frequencies Ͼ40 kHz. We thus simulated the frequency spectrum of a signal as being perceived at medium sender-receiver distances, where ultrasonic frequencies are strongly attenuated (Keuper et al, 1986;Romer and Lewald, 1992).…”

Asymmetrical integration of sensory information during mating decisions in grasshoppers

“…In our case, nonattractive syllables exhibit salient features that reliably indicate "wrong male"-a large weight should therefore be assigned to negative information. In contrast, the differences between the attractive syllables of conspecifics of different quality rely on more subtle features of the song that are prone to be distorted by environmental noise (33,38,39). Hence, positive information tends to be less reliable and should therefore be weighted less.…”

Lack of correlation between vertical distribution and carrier frequency, and preference for open spaces in arboreal katydids that use extreme ultrasound, in Gorgona, Colombia (Orthoptera: Tettigoniidae)

“…At ground level and understory (0-5m) acoustic signals tend to suffer more attenuation than in the upper parts (Marten, Quine & Marler, 1977;Römer, 1993;Römer & Lewald, 1992). At a height of ca.…”