Reproductive evolution and morphology in Australian thynnine wasps

Abstract

Thynnine wasps (Hymenoptera: Tiphiidae: Thynninae) are a remarkable group of insects. They display extreme sexual dimorphism, and copulation typically occurs "on the wing", with the female suspended solely by her genitalia as she is carried by the male. This mating behaviour and genital coupling mechanism has resulted in a high number of mating pairs preserved in copula in collections. Thus, thynnids offer a rare opportunity to study the functional interactions between male and female genitalia, in a comparative framework across multiple species. This forms the central theme of this thesis. The first chapter provides a comprehensive workflow for manipulating and visualising 3Ddata, which includes basic and advanced options for producing images, videos and interactive 3D-PDFs, from both volume and surface-mesh renderings (Semple, Peakall & Tatarnic 2019). The aim was to make the processing, visualisation and presentation of 3D-data easier, thereby encouraging more researchers to utilise 3D-imaging. We discuss the importance of visualisation for quantitative analysis of invertebrate morphology from 3D-data, and provide example figures from micro-CT scans of thynnine wasps illustrating the different options for generating 3D-figures for publication. The second chapter aims to improve our knowledge of the phylogenetics of the Thynninae, in order to take full advantage of this study system for evolutionary research. We estimated a genus-level phylogeny of the Australian Thynninae, using high-throughput DNA sequencing of Ultra-Conserved genomic Elements (UCEs). This provided the first, broad, genus-level phylogeny of the Australian Thynninae, and will enable new research on the diversification, biogeography and evolution of thynnines. Chapter three explores the utility of 3D-imaging for studies on anatomy, functional morphology, and reproductive incompatibility between species. Here we focused on the thynnine genus Catocheilus, and hypothesised that the functional requirement of supporting females during in-flight mating has resulted in relatively-conserved coupling structure morphology. We used microCT-based 3D-imagery of Catocheilus spp. to describe the functional morphology of their genitalia, construct an anatomical atlas of their coupling structures, and perform a digital simulation of physical compatibility between species. The fourth and last data chapter stands as the culmination of the former three, bringing together 3D imaging, phylogenetics and morphology. In thynnine wasps, in-flight mating and female-feeding by males has created a dual role for the coupling structures, and a complex mixture of different selective pressures acting on each component. Here we used 3D geometric morphometrics to perform a comparative analysis of shape variation in coupling structures across the Thynninae. We predicted that the morphology of thynnine coupling structures would be affected by both the functional constraints of multiple roles, as well as the mutual fitness benefits of the mating and feeding flight. Our results confirm that function, mechanical constraints and coevolution have all likely influenced the morphological evolution of individual coupling components in thynnines. The last section provides a brief summary of the current uses and future directions of 3D imaging in invertebrates, with references to some of the more recent advances in visualization of 3D data.