Biodiversity and Biogeography of Myrmecosymbioses and Vanuatuan Ants

Biogeography places the geographical distribution of biodiversity in an evolutionary context. Ants (Hymenoptera: Formicidae), being a group of ubiquitous, ecologically dominant, and diverse insects, are useful model systems to understand the evolutionary origins and mechanisms of biogeographical patterns across spatial scales. On a global scale, ants have been used to test hypotheses on the origin and maintenance of the remarkably consistent latitudinal diversity gradient where biodiversity peaks in the equatorial tropics and decreases towards the poles. Additionally, ants have been used to posit and test theories of island biogeography such as the mechanisms of the species-area relationship, being the increase of biodiversity with cumulative land area. However, there are still unanswered questions about ant biogeography such as how specialized life histories contribute to their global biogeographical patterns. Furthermore, there remain island systems in the world’s biodiversity hotspots that harbor much less ant species than predicted by the species-area relationship, which potentially suggests a place ripe for discovery. In this dissertation, I use natural history, taxonomic, geographic, and phylogenetic data to study ant biodiversity and biogeography across spatial scales. First, I study the global biodiversity and biogeography of a specialized set of symbiotic interactions between ant species, here referred to as myrmecosymbioses, with an emphasis on social parasitism where one species exploits the parental care behavior and social colony environment of another species. In addition to characterizing a new myrmecosymbiosis, I use a global biogeographic and phylogenetic dataset to show that ant social parasitism is distributed along an inverse latitudinal diversity gradient where species richness and independent evolutionary origins of social parasitism peak within the northern hemisphere where the least free-living ant diversity exists. Second, I study the unexplored ant fauna of the Vanuatuan archipelago in the South Pacific. Using approximately 10,000 Vanuatuan ant specimens coupled with phylogenomics, I fill in a historical knowledge gap of South Pacific ant biogeography and demonstrate that the Vanuatuan ant fauna is a novel biodiversity hotspot. With these studies, I provide insights into how specialized life histories and unique island biotas shape the global distribution of biodiversity in different ways, especially in the ants.