title: On the macroevolution of antipredator defence
Creators: name: Arbuckle, Kevin
Publisher: name: University of Liverpool Repository
Year: 2015

description: This thesis aims to improve our understanding of the macroevolutionary implications of antipredator defences, particularly with regard to how defence impacts biodiversity (including both species and trait diversity). To do this I took a phylogenetic comparative approach and used multiple study systems in an attempt to ensure the generality of my work. I begin by investigating how chemical defence and protective coloration influence ecology by testing for life history and ecological correlates of these defences (Chapter 1). Upon finding evidence for an increased niche space in chemically-defended species, and to some degree in conspicuously-patterned species, I explore whether this leads to increased diversification by increasing speciation rates and/or lowering extinction rates (Chapter 2), as also predicted by escape-and-radiate theory (a major and highly influential framework for the macroevolution of natural enemy interactions). Both conspicuous coloration and chemical defence increased speciation rates, but extinction rates were also raised in chemically-defended lineages, leading to a reduction in net diversification. Macroevolutionary extinction rates may or may not be related to contemporary extinction risk, but if they are then there may be conservation implications by allowing prediction of threat status of species with limited direct information. Consequently, in Chapter 3 I asked whether chemically-defended species are more threatened than those lacking such a defence. In accordance with the macroevolutionary results from Chapter 2, I found that chemical defence is indeed associated with a higher extinction risk even amongst contemporary species. In addition to factors that promote diversity, in this thesis I also investigated convergent evolution as a means of constraining diversity of phenotypic traits, using mimicry as a case study for antipredator defences. Many antipredator defences are convergent to some degree, with examples in the repeated evolution of chemical defences and warning coloration as well as independently derived similarity in protective mimicry. However, methods of quantifying the strength of convergent evolution are lacking, not to mention a conceptual framework to define 'strength' in this context, I began by developing a new method to do this which I called the Wheatsheaf index (Chapter 4). Subsequently, I (in collaboration with a colleague, Amanda Minter) also designed software in the form of an R package (called 'windex') to enable user-friendly implementation of the Wheatsheaf index in a familiar statistical environment to many biologists (Chapter 5). In the final data chapter of this thesis, I apply this method in a case study to explore the patterns of phenotypic convergence that result from the evolution of Batesian and Müllerian mimicry complexes. I find that these two types of protective mimicry are generally characterised by convergence in different broad types of traits, but that the specific traits which converge in a given mimicry complex are less predictable (Chapter 6). Overall, this thesis provides novel insights into the evolutionary patterns and consequences of antipredator defences, develops a framework and methods for the analysis of convergent evolution, and suggests further avenues of research for future studies.