Comparative analysis of fertility signals and sex-specific cuticular chemical profiles of Odontomachus trap-jaw ants.

Abstract

The lipid mixture that coats the insect cuticle contains a number of chemical signals. Mate choice in solitary insects is mediated by sexually dimorphic cuticular chemistry, whereas in eusocial insects, these profiles provide information through which colony members are identified and the fertility status of individuals is assessed. Profiles of queens and workers have been described for a number of eusocial species, but there have been few comparisons of fertility signals among closely related species. Additionally, sexual dimorphism in cuticular lipid profiles has only been reported in two species of ants. This study describes the cuticular chemical profiles of queens, workers and males of three species of Odontomachus trap-jaw ants: O. ruginodis, O. relictus and O. haematodus. These are compared with fertility signals and sexually dimorphic profiles already described from O. brunneus. We report that fertility signals are not conserved within this genus: chemical compounds that distinguish queens from workers vary in number and type among the species. Furthermore, the compounds that were most abundant in cuticular extracts of O. ruginodis queens relative to workers were novel 2,5-dialkyltetrahydrofurans. Bioassays of extracts of O. ruginodis queens indicate that the dialkyltetrahydrofuran and hydrocarbon fractions of the profile are likely to work synergistically in eliciting behavioral responses from workers. In contrast, cuticular lipids that distinguish males from females are more conserved across species, with isomeric and relative abundance variations comprising the main differences among species. Our results provide new insights into how these contact chemical signals may have arisen and evolved within eusocial insects.