Drivers of the evolution of gregarious behaviour in larval Lepidoptera

Abstract

To evolve, and remain adaptive, social behaviours must have a positive impact on overall individual fitness. However, these adaptive benefits may not be immediately apparent due to an array of interactions with other ecological traits, which can depend on a lineage’s evolutionary past and the mechanisms controlling group behaviour. Here, I use lepidopteran larvae as a model system to investigate the evolution of social behaviour, utilising their diversity in social behaviour to explore critical interactions between ecological, morphological and behavioural traits. I perform powerful phylogenetic comparative analyses, testing the evolutionary relationships between larval social behaviour and a number of key morphological and ecological traits. I also perform the first phylogenetic study into the molecular functions underpinning social behaviour in larvae. I find extensive evidence of the phenotypes which make the evolution of larval gregariousness more likely, showing that the behaviour typically evolves after the acquisition of facilitative traits, such as aposematism. I further explore relationships between larval appearance and behaviour, and identify differential colour pattern use between solitary and gregarious aposematic larvae. Additionally, I find that gregarious larvae are more specialised in their host plant use compared to solitary larvae, and that this specialisation likely occurs before a transition to the behaviour. Finally, I reveal clear differences in gene expression between larvae that vary in social behaviour, as well as evidence for a convergent molecular association with the gregarious phenotype, including genes involved in immune system function and increased feeding behaviour. My thesis reinforces the close evolutionary relationship between larval gregariousness and aposematism, whilst highlighting additional questions surrounding the roles of key morphological and ecological factors in the evolution of gregarious behaviour. Furthermore, I identify several genes with putative, convergent links to larval gregariousness, providing a foundation from which study into the mechanistic basis of larval social behaviour can continue.

Date of Award	5 Dec 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Stephen H Montgomery (Supervisor) & Innes C Cuthill (Supervisor)