Plasticity of signaling and mate choice in a trilling species of the Mecopoda complex (Orthoptera: Tettigoniidae)

Abstract

Males of a trilling species in the Mecopoda complex produce conspicuous calling songs that consist of two motifs: an amplitude-modulated motif with alternating loud and soft segments (AM-motif) and a continuous, high-intensity trill. The function of these song motifs for female attraction and competition between males was investigated. We tested the hypothesis that males modify their signaling behavior depending on the social environment (presence/absence of females or rival males) when they compete for mates. Therefore, we analyzed acoustic signaling of males in three different situations: (1) solo singing, (2) acoustic interaction with another male, and (3) singing in the presence of a female. In addition, the preference of females for these song motifs and further song parameters was studied in two-choice experiments. As expected, females showed a preference for conspicuous and loud song elements, but nevertheless, males increased the proportion of the AM-motif in the presence of a female. In acoustic interactions, males reduced bout duration significantly compared to both other situations. However, song bouts in this situation still overlapped more than expected by chance, which indicates intentionally simultaneous singing. A multivariate statistical analysis revealed that the proportion of the AM-motif and the duration of loud segments within the AM-motif allow a reliable prediction of whether males sing in isolation, compete with another male, or sing in the presence of a female. These results indicate that the AM-motif plays a dominant role especially in close-range courtship and that males are challenged in finding a balance between attracting females and saving energy during repeated acoustic interactions.Significance statementMales of acoustic insects often produce conspicuous calling songs that have a dual function in male-male competition and mate attraction. High signal amplitudes and signal rates are associated with high energetic costs for signal production. We would therefore predict that males adjust their signaling behavior according to their perception of the social context. Here we studied signal production and mate choice in a katydid, where males switch between loud and soft song segments in a dynamic way. Additionally, we examined the attractiveness of different song elements in female choice tests. Our results show how males of this katydid deal with the conflict of remaining attractive for females and competing with a costly signal with rivals.

Evolutionarily conserved coding properties favour the neuronal representation of heterospecific signals of a sympatric katydid species

“…These motifs differed mainly in their amplitude, but also in the fine structure of the syllables. While the AM-motif consisted of alternating loud and soft segments, the trill had a continuously high amplitude of 103 dB SPL when the signalling individual was 15 cm from the male, in contrast to 86 dB SPL for soft segments (Krobath et al 2017 ). Both the loud song segments in the AM-motif and the trill consisted of a soft syllable followed by two syllables with high amplitude, a stereotypical pattern that was repeated with a period duration of 30 ms for more than 100 s. We used this trill pattern as conspecific stimulus in our playbacks.…”

“…Males of the one species produce chirps with regular inter-chirp intervals of about 2 s (Hartbauer et al 2012 ; Siegert et al 2013 ); they are identical to those of “species S” described by Sismondo ( 1990 ). The song of the other species consists of an amplitude-modulated song motif, followed by a long-lasting trill (Krobath et al 2017 ). In the following text, both species are referred to as “chirper” and “triller” (see photographs in Fig.…”

The heterospecific calling song can improve conspecific signal detection in a bushcricket species

“…The SPL of the receiver was set to 81 dB at a distance of 1 m, a value that corresponds to the average peak SPL of M. elongata males measured at a distance of 1 m (Hartbauer et al, 2014). The amplitude of the 10 kHz signal was simulated assuming an amplitude of 85 dB SPL and measured at a distance of 1.2 m (corresponds to 103 dB measured at 15 cm; see Krobath, 2013). A hearing threshold of 52 dB SPL (−1 dB subthreshold) was simulated for the 5 kHz signal which corresponds to the hearing threshold for 2 kHz signals.…”

Bioacoustics and systematics of Mecopoda (and related forms) from South East Asia and adjacent areas (Orthoptera, Tettigonioidea, Mecopodinae) including some chromosome data

“…Song The most detailed study of the song was undertaken by Krobath (2013;Krobath et al 2017) under the name ‚trilling species of the Mecopoda complex'. At intervals of many minutes, the males produce calling bouts which last several minutes and start with an alternation between soft and loud trilling parts and end in a continuous long loud trill (Krobath 2013;Krobath et al 2017). The stridulatory movements differ between soft and loud parts.…”