From Genes to Communities: An Integrative Approach to the Evolution of Varanidae

Abstract

Why do organisms look the way they do? Why do they live where they do? Why are some groups more diverse than others? These basic questions are often addressed at different scales using a particular set of methods. For example, the first question could be addressed by either looking at phenotypes across a phylogeny in a comparative framework or by looking at fine scale variation across the landscape within a species. However, it has been challenging to build a conceptual and methodological bridge linking ecological processes and population dynamics with evolutionary and biogeographic patterns above the species level. In this thesis, I present research spanning a broad range in the continuum between micro- and macroevolution. Appropriately, my study system is monitor lizards (Squamata: Varanidae), the terrestrial vertebrate genus showing the largest disparity in body size. These charismatic reptiles display notable variation in species richness, morphology, and ecology across the three continents and numerous oceanic islands they call home. I gathered large molecular, morphological, and environmental datasets and analysed them using process-based methods linking ecological and population-level processes with speciation and macroevolutionary patterns. I used this integrative approach to identify the drivers of genetic, phenotypic, and lineage diversification in Varanidae at different evolutionary scales. In Chapter I, I show that the diversification dynamics of three endemic varanid radiations in Indo-Australasia have been dictated by a combination of geography and interspecific interactions. In Chapter II, I demonstrate that ontogenetic lability is behind morphological diversification in varanids and their kin, and that ontogenetic ecological shifts in ecology explain some of the ontogenetic variation in the group. In Chapter III, I used a comprehensive approach to uncover signs of ancient hybridization between the iconic Komodo dragon and a group of Australian varanids, corroborating the Australian origin of the former. In Chapter IV, I evaluate species limits in spiny-tailed monitors and present genomic and phenotypic evidence for local adaptation despite extensive gene flow. Together, these chapters show how the integration of multiple sources of evidence can offer insight into the long-term evolutionary consequences of developmental, ecological, and population-level processes. Show more