Evidence for individual variation and the role of personality in the assessment strategies of Teleogryllus commodus contests

Abstract

Evolutionary game theory and assessment strategy models have been used to try to understand animal decision making processes during male-male contests. However, this has often led to mixed or inconclusive results. This may be due to various factors including that current analysis frameworks are unable to detect individual variation in assessment strategy use, that personality may affect assessment strategy use via underlying mechanisms/ behavioural syndromes, or that animals are able to switch assessment strategies as contests escalate. However, these possible explanations for individual and population variation in contest dynamics have yet to be extensively explored. In this thesis I firstly assessed whether Australian black field crickets (Teleogryllus commodus) display consistent inter-individual variation (personality) in four different contexts. I then assessed whether these four behaviours are linked, forming a behavioural syndrome. The four behaviours measured were general activity, boldness in a novel environment, boldness after a predation-risk event and aggression towards a conspecific. Inter-individual variation was repeatable for general activity, boldness in a novel environment and aggressiveness, but not for boldness after a predation risk. Therefore, there was evidence for personality in T. commodus. However, none of the behaviours were correlated across contexts, indicating that there is no behavioural syndrome linking these four particular behaviours. Next, I assessed which assessment strategy Australian black field crickets (Teleogryllus commodus) use during male-male conflict, and whether there is any individual variation in the use of assessment strategy within the population. I then assessed whether T. commodus switch assessment strategies during contests by analysing each phase of the contest individually. Finally, I assessed whether boldness affects the assessment strategy employed by individuals during conflict. To assess the assessment strategy used by T. commodus I used novel methodology proposed by Chapin et al., (2019), and compared the results to those when using the more traditional methodology proposed by Taylor and Elwood (2003). The results from the Taylor and Elwood (2003) analysis were inconclusive. However, the Chapin et al., (2019) analysis clearly showed that T. commodus uses a mix of assessment strategies, that there is individual variation in assessment strategy use in my population of T. commodus and that switching of assessment strategy is possibly occurring between phases of the contest. Boldness also did not appear to have an effect on the assessment strategy used in this population. As the first study to empirically apply the Chapin et al., (2019) methodology, my results demonstrate how the methodology can be applied to real animals and the improvements this could provide to the field. I believe this thesis demonstrates how important it may be to assess for individual variation in assessment strategy use, switching of assessment strategies between phases of conflict and the effect of personality on individual assessment strategy use, particularly in species that have previously had inconclusive results.