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

I. Krobath,H. Römer,M. Hartbauer

doi:10.1007/s00265-017-2381-6

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.

Highlights

Males of many acoustic insect species produce conspicuous calling songs to attract females from a distance and, at the same time, compete with rival males
Because the two song motifs could potentially be directed toward a different audience (i.e., either female or rival male(s)), we studied the calling songs produced by males in the presence of females and measured the amount of time spent in singing the AM-motif and trill
Because the same set of males was used in the isolation and acoustic interaction experiments, we developed a GLMER model using male ID as a random term to predict the social singing situation

Summary

Introduction

Males of many acoustic insect species produce conspicuous calling songs to attract females from a distance and, at the same time, compete with rival males. These calling songs often exhibit high amplitudes and signal rates, which are song parameters associated with high costs. For example in Hyla microcephala, females prefer multi-note over single-note calls, which stimulates the males to increase both the call rate and number of call notes in a chorus situation (Schwartz 1986) Such competitive signaling is associated with higher energetic demands (Wells and Taigen 1989). In P. pustulosus, the presence of females immediately affects the males’ calling song production, driving increased signal complexity (Akre and Ryan 2011)

Methods

Results

Conclusion