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

## TL;DR

This study shows that more complex social behavior in insects does not necessarily lead to more complex chemical communication.

## Contribution

The first study to combine chemical and genetic data across all levels of sociality in Blattodea insects.

## Key findings

- Chemical complexity does not consistently correlate with social complexity in Blattodea.
- Transcriptomic diversity of chemical biosynthesis genes also does not reflect social organization levels.
- Results challenge the assumption that social complexity increases chemical profile sophistication.

## Abstract

Eusocial insects, such as ants and termites, are characterized by high levels of coordinated social organization. This is contrasted by solitary insects that display more limited forms of collective behavior. It has been hypothesized that this gradient in sociobehavioral 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 insects. We assessed CHC complexity and divergence between our studied taxa 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 social complexity, nor did the overall chemical divergence or transcriptomic repertoire of CHC biosynthesis genes reflect on the levels of social organization. Our results challenge the assumption that increasing social complexity is generally reflected in more complex chemical profiles and point toward the need for a more cautious and differentiated view on correlating complexity on a chemical, genetic, and social level.

We assessed the long‐standing hypothesis that chemical profile complexity increases with levels of sociality in the insect order Blattodea investigating solitary as well as eusocial species. Strikingly, we could not confirm any consistent correlative patterns between chemical, transcriptomic, and social complexity. Thus, our results challenge the assumption of a general correlation between increasing social complexity and chemical profile sophistication, which we present here for the first time on a scale uniting both chemical and genetic data in an insect order reflecting all levels of sociality.