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.