The interplay between social and environmental plasticity in the rapid adaptation of a Hawaiian field cricket (Teleogryllus oceanicus)

Abstract

The role of phenotypic plasticity in genetic adaptation has been at the centre of a decades long debate. Recent research has revealed that the potential for plasticity-led adaptation is highly conditional, dependant on the intrinsic characteristics of a plastic response and the selection pressures acting on it. However, the fact that the potential for plasticity-led adaptation is susceptible to multiple environmental conditions, given that phenotypes are expressed in an interdependent ecological and social context, has been inadvertently neglected. In this thesis, I investigate the intricate relationship between social and environmental plasticity in the rapid adaptation of the Hawaiian Field Cricket (Teleogryllus oceanicus). Ancestrally reliant on acoustic signals for sexual advertising, selection from an acoustically orienting parasitoid fly (Ormia ochracea) has led to the emergence of a silent male morph (induced by the flatwing mutation). Adaptive behavioural adjustments in the new morph, coupled with permissive female choice, are thought to have accommodated the absence of an important sexual signal. Flatwing males show higher propensity to engage in phonotactic behaviour and socially-plastic locomotory activity, facilitating encounters with conspecifics. Here, I investigate how different components of the abiotic and social environments interact to shape the expression of traits that promote flatwing evolution at the behavioural and genetic level. Through dietary and social environment manipulation, Chapter 2 revealed that direct and indirect, genetic and environmental effects influenced female mating behaviour and male courtship. In Chapter 3, I identified the genetic substrate involved in socially-plastic adaptations in flatwing males. Chapter 4 showed that the outcome of social interactions between females was dependent on multiple social environment components, and Chapter 5 revealed that previously observed female preferences dissipate in a group context. These findings underscore the importance of considering multiple sources of plasticity and their interactions to fully grasp the evolutionary consequences of phenotypic plasticity.