Heads up: sexual dimorphism in house crickets (Acheta domesticus)

Abstract

Many species are sexually dimorphic because of differential selection on each sex. In many species, males tend to have exaggerated traits or larger body size compared with females. In house crickets ( Acheta domesticus L., 1758), the males defend resources and compete for mates by engaging in a striking visual display sequence that includes mandible flaring, where males spread their mandibles wide open. This behavior presumably acts only in males as a visual signal of body size and as an indicator of the willingness to fight, as females do not exhibit this behavior. We tested the hypothesis that sex differences in the signals used for aggressive interactions will lead to sex differences in the morphology of the head in house crickets. To test this hypothesis we made linear measurements of body and head sizes on males and females and utilized geometric morphometric methods to reconstruct sex differences in shape. We also compared the total pigmented area of the faces of males and females. Males had larger heads with proportionally more pigmented area than females and there were significant shape differences. In addition, allometric relationships between head size and body size indicated that head size increases faster than body size in males. Geometric morphometric analysis indicated that the shape differences result in an exaggeration of the mandibular area in males compared with females. These data suggest that the differential selection acting on males and females can lead to differences in size, shape, and pigmentation related to signal structure and function.