The phasmatodean tree of life - Resolving evolutionary patterns of diversity and disparity in a mesodiverse insect lineage

Abstract

Phasmatodea comprises a group of large terrestrial herbivores commonly known as stick and leaf insects. Their name reflects their impeccable masquerade as plant parts, with most species exhibiting an elongated and slender body imitating twigs, while others may resemble bark, moss, lichen or leaves. Counting among the mesodiverse groups of insects, their morphological diversity is represented by more than 3400 described species with the number of new species discovered steadily growing – even for well-explored regions. However, unmethodical classification over the last century resulted in a highly chaotic taxonomy. The use of molecular phylogenetics has revealed itself as a powerful tool to revise the traditional classification showing that morphological resemblance among phasmatodean taxa appears to have often resulted from convergently evolved traits rather than from common ancestry. Since recent phylogenetic analyses continued to present discordant results regarding specific lineages and did not include all taxonomic groups, further inferences of phasmatodean phylogenetic relationships are needed. In order to resolve the observed discrepancies and to reassess proposed phylogenetic relationships, I performed phylogenetic analyses based on a set of three nuclear and four mitochondrial genes and an increased taxon sampling covering hitherto underrepresented lineages. These resulting well-supported phylogenies provided better insights into the phylogenetic relationships within the ground-dwelling Heteropterygidae (Chapter 1) as well as the leaf-mimicking Phylliidae (Chapter 2), and allowed to interpret their life history regarding biogeographical patterns and evolutionary processes. A complete overview of the entire phasmatodean phylogeny and the distribution of characters involved in flight further permitted to draw conclusions about the possibility of regaining wings and ocelli (Chapter 3): The results highly support that wings and ocelli were absent in the common ancestor of (Eu)Phasmatodea and that wings were repeatedly regained in subordinated groups. The fact that ocelli are not present in all winged and volant taxa but only occur in closely related species within only five of the major lineages is another indication of trait reacquisition, because the opposing hypothesis would imply the repeated loss of these structures while wings and flight are retained. In summary, the research presented herein greatly improves our understanding of the phylogenetic relationships of Phasmatodea and provides new insights into their evolutionary histories. The conclusions will serve as guidelines for interpreting morphological traits and their evolution, and the results provide a solid basis for future studies on phasmatodean systematics and taxonomy as well as for research questions on evolutionary patterns and processes.