Tactical adjustment of sexual display behaviour: models and tests in invertebrates

Abstract

Behavioural sexual displays are found in a wide array of taxa across the animal kingdom and are used in intra-sexual competitive interactions and to increase the chances of mating. Sexual display behaviours are often tactically adjusted to a displayer's context, and this adjustment is thought to minimise the costs of displaying while maximising the benefits. However, signallers often display in proximity to rival signallers and the cost:benefit ratio of each signaller's behavioural strategy is not independent. Therefore, we would expect signallers to adjust their behaviour in response to the social context in which they are signalling. There is research showing that signallers tactically adjust their behaviour in response to the behaviour of potential mates, and that this also occurs in response to the presence or absence of rivals. However, there is little research showing how the attractiveness and behaviour of rivals affects signaller behaviour. We also do not know how a male's own morphological ornaments (which are often used as part of display behaviours) interact with tactical display adjustment. To address these gaps in our knowledge, I used long-term, large-scale observational data from Gryllus campestris in chapter 2 to determine how males adjust their behaviour in response to signalling rivals. I found that males adjust their signalling behaviour in response to signalling rivals, and the direction of this adjustment is dependent on the distance to the signalling rivals. In chapter 3, I developed a stochastic dynamic game model to predict how altering the signalling context affects the predicted evolutionarily stable signalling strategy. This model predicts that signalling strategies are affected by changes to potential mate availability and the attractiveness and competitive ability of rival males in the population. In chapter 4, we used observational data from a species of fiddler crabs (Afruca tangeri) to investigate how a male's behavioural adjustment in response to females is moderated by the size of his major claw. We found no evidence that males with different sized claws adjust their courtship behaviour differently in response to females. However, we do find that males with smaller claws spend more time in their burrow when females are further away, relative to males with larger claws. In chapter 5, we created a biomimetic robotic male fiddler crab which allowed us to experimentally manipulate the social environment of a wild male and record changes in behaviour as a response. We found that bouts of signalling were longer on average when the robotic rival was waving at a fast speed, and that males were less likely to enter and spend time in their burrow when the robotic rival was waving at any speed. In chapter 6, I discuss my findings, the broader implications of each of the research projects, and areas for future development.