Chemical and transcriptomic diversity do not correlate with ascending levels of social complexity in the insect order Blattodea

Abstract

Eusocial insects, such as ants and termites, are characterized by high levels of coordinated social organization. This is contrasted by solitary insects, which display more limited forms of collective behavior. It has been hypothesized that this gradient in socio-behavioral sophistication is positively correlated with chemical profile complexity, due to a potentially increased demand for diversity in chemical communication mechanisms in insects with higher levels of social complexity. However, this claim has rarely been assessed empirically. Here, we compare different levels of chemical and transcriptomic complexity in selected species of the order Blattodea that represent different levels of social organization, from solitary to eusocial. We primarily focus on cuticular hydrocarbon (CHC) complexity, since it has repeatedly been demonstrated that CHCs are key signaling molecules conveying a wide variety of chemical information in solitary as well as eusocial insect species. We assessed CHC complexity and divergence between our studied species of different social complexity levels as well as the differentiation of their respective repertoires of CHC biosynthesis gene transcripts. Surprisingly, we did not find any consistent pattern of chemical complexity correlating with the degree of social complexity, nor did the overall chemical divergence or transcriptomic repertoire of CHC biosynthesis genes reflect on the levels of social complexity. Our results challenge the assumption that increasing social complexity is generally reflected in more complex chemical profiles and point towards the need for a more cautious and differentiated view on correlating complexity on a chemical, genetic, and social level.