Investigating the behavioural consequences of evolutionary signal loss in the context of a naturalistic environment

Abstract

The evolutionary loss of sexual traits is thought to be common, but empirical examples of it occurring are rare. In this thesis, I investigate social and other behavioural factors that might facilitate signal loss. Specifically, I took an empirical approach to evaluate the ways in which the loss of a long-range acoustic signal, song, alters the mating dynamics and social behaviours of individuals in affected populations. This confronts a methodological challenge in behavioural research – the difficulty of observing and measuring behaviours from within a natural context - a context that includes the physical and social environmental conditions in which they evolved. To overcome this challenge and to study the consequences of sexual signal loss, I developed a novel tracking system to monitor, in a laboratory setting that mimicked field-like conditions, the behaviour of a cricket species in which some males have lost the ability to sing. In populations of the Hawaiian field cricket, Teleogryllus oceanicus, silent ‘flatwing’ males carry mutations that remove key wing structures, eliminating acoustic signalling and affording protection against an acoustically-orientating parasitoid fly (Ormia ochracea). This also removes their ability to attract females via song. Despite this, largely silent populations persist in the wild. Using the developed tracking system to monitor groups of individually-tagged crickets, I show how behavioural plasticity of both males and females might accommodate the disappearance of song and mitigate negative effects on reproductive fitness. This appears to be achieved by increased movement activity and changes to key social interaction dynamics. My results highlight the flexible and potentially compensatory nature of animal behaviour in facilitating rapid evolutionary change.