Allometry of male sound-producing structures indicates sexual selection on wing size and stridulatory teeth density in a bushcricket

The majority of bushcricket species (Insecta: Orthoptera: Tettigoniidae) use acoustic signals for mate attraction. Song production and the sound-producing structures, therefore, can be argued to be under sexual selection. The sound-producing structures might determine differences in the acoustic parameters of male songs, like the fundamental frequency. We investigated the morphology and scaling relationships of the sound production organs in males of the bushcricket Poecilimon ampliatus. Selection acting on morphological traits can be inferred from allometric relationships. Our results show that heavier and larger males have bigger sound-producing organs: wing area scales positively with body mass as well as with body size. The length of the stridulatory file and the stridulatory teeth length both increase with wing area. In contrast, the number and density of teeth on the stridulatory file decrease in heavier males. As a result, males with larger wings and longer stridulatory files have a reduced teeth density. Positive isometric scaling was detected for the length of stridulatory teeth, as well as negative isometry for teeth number and teeth density. Wing area in turn seems to be under positive sexual selection, as the relationship of wing size on male body size show a steep positive slope (beta = 2.4). The morphological results indicate positive selection on sound-producing structures and are in line with the female preference for heavier males in mate choice experiments.