Does fluctuating asymmetry of hind legs impose costs on escape speed in house crickets (Acheta domesticus)?

Abstract

Fluctuating asymmetry (FA) is often thought to be an indicator of developmental stability—an individual’s ability to resist environmental and genetic stress during development—and thus demonstrates phenotypic quality. Research on the influence of FA on locomotion has often found that high FA in legs and wings impedes locomotor performance. Crickets rely on their six limbs to flee from predators and parasitoids. Hind legs are of particular importance during escape as they contribute to running speed. FA research overwhelmingly focuses on its impact on sexual selection, with little on locomotion and only one study of the impact of FA on invertebrate locomotion. Here, we examined the effect of FA in hind legs on the escape speed of house crickets (Acheta domesticus) and the locomotor costs of hind limb autotomy. Unexpectedly, our findings indicate that FA of hind legs have no influence on the escape speed of either male or female A. domesticus. This is inconsistent with most research conducted on FA and vertebrate locomotion that indicates FA negatively impacts locomotion, but is consistent with the only research examining FA and invertebrate locomotion. Our other findings were more congruent with the literature on other Orthoptera, as body size was found to have an influence on the escape speeds of intact females and those that lost two hind limbs. Whilst our results indicate that FA did not influence locomotion, this may not be the case for other invertebrate taxa where variation in FA may have an important role in natural selection.