Do ant mimics imitate cuticular hydrocarbons of their models?

Abstract

Myrmecomorphy, or ant mimicry, is a frequent type of Batesian mimicry among invertebrates. Myrmecomorphic species possess colour pattern and morphological resemblance to ants. Mimics associate closely with models that are dangerous to the mimics. Therefore, mimics must have been under strong selection to evolve adaptations that increase their survival among foraging ants. The imitation of intraspecific chemical signals on their cuticle could provide protection against ants. We studied whether myrmecomorphic spiders imitate cuticular hydrocarbons of their models. We chose five myrmecomorphic spider species (Liophrurillus flavitarsis, Micaria sociabilis, Myrmarachne formicaria, Phrurolithus festivus, Zodarion alacre) from four families and compared their cuticular hydrocarbon profiles to those of their ant models (Aphaenogaster senilis, Liometopum microcephalum, Formica rufibarbis, Lasius platythorax, Formica subrufa). In addition we conducted experiments in which we tested the behavioural response of model ants to mimics and nonmimetic spiders. We found that the hydrocarbon profiles of mimics were generally not similar to the hydrocarbon profiles of their ant models, except for certain compounds (octacosane and nonacosane). Overall, there was a higher similarity in profiles among mimics than among ant models. In the experiments, ants attacked more nonmimetic species and three mimetic species but fewer of the mimics M. formicaria and Z. alacre. The difference is attributed to the similarity between the two mimics and the ants in long-chain hydrocarbons. Our results show that ant-mimicking spiders must use other means to evade their models to increase their survival among model ants, such as behavioural avoidance.