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.

Comparative transcriptomics of social insect queen pheromones

“…These signals can affect the behaviour of other colony members, e.g. by attracting workers 3 , eliciting submissive behaviour 4 , modulating aggression 5 , or inhibiting production of new queens 6,7 . Queen pheromones also have long-lasting effects on individuals that encounter them, including reducing female fecundity 1 , influencing the rate at which workers progress to different tasks with age 8 , and altering workers’ capacity to learn 9 .…”

Conservation of Queen Pheromones Across Two Species of Vespine Wasps

“…In contrast to the honeybee Apis mellifera, in which much work has focused on the queen's mandibular pheromones and their major constituent 9-oxo-(E)-2-decenoic acid (9-ODA), it has been shown that cuticular hydrocarbons (CHCs) likely act as conserved queen signals across several other lineages of social Hymenoptera (Holman et al 2013;Oi et al 2015a;Oliveira et al 2015;Van Oystaeyen et al 2014). In particular, bioassays have shown that specific queen-characteristic hydrocarbons inhibit worker reproduction across a variety of social insect taxa, including the bumblebee Bombus terrestris (Holman 2014;Van Oystaeyen et al 2014), the common wasp Vespula vulgaris (Van Oystaeyen et al 2014), and several species of ants (Holman et al 2010(Holman et al , 2013(Holman et al , 2016aSmith et al 2016;Van Oystaeyen et al 2014). These results demonstrate that specific CHCs have evolved to become queen pheromones across at least three independent origins of eusociality (Oi et al 2015a;Oliveira et al 2015;Van Oystaeyen et al 2014).…”

“…On the other hand, there are examples where fertility signals do not appear to be conserved within a particular genus. Most notably, in Odontomachus trap-jaw ants, a comparison across three congeneric species showed that fertility signals were not conserved, with chemical compounds from queens and workers differing in number and type among the species analyzed (Smith et al 2016). It also was shown that the chemical context in which the signal is perceived can be important for proper recognition of fertility signals (Smith et al 2015).…”

Queen Recognition Signals in Two Primitively Eusocial Halictid Bees: Evolutionary Conservation and Caste-Specific Perception

“…Despite this, several additional studies have shown that compounds other than CHCs have a function as queen signals in, for example, the honeybee Apis mellifera and the termite Reticulitermes speratus [16][17][18]. Moreover, chemical analyses and bioassays in various trap-jaw ant species of the genus Odontomachus have revealed a more complex picture, with CHCs and other compounds probably functioning synergistically as queen signals, although these signals are also more divergent among the different species of the same genus [19]. Indeed, various species of Odontomachus have been shown to exhibit different chemical compounds as fertility signals characterizing the queens, which indicates that queen signals are even not conserved within this genus [19].…”

“…Moreover, chemical analyses and bioassays in various trap-jaw ant species of the genus Odontomachus have revealed a more complex picture, with CHCs and other compounds probably functioning synergistically as queen signals, although these signals are also more divergent among the different species of the same genus [19]. Indeed, various species of Odontomachus have been shown to exhibit different chemical compounds as fertility signals characterizing the queens, which indicates that queen signals are even not conserved within this genus [19]. However, most of these studies dealing with queen signals have focused on species with a highly derived eusocial behavior and obvious caste-specific differences in the composition of chemical compounds.…”