Insect molecular phylogenetics: The evolution of nonflying aerodynamic locomotion and larval feeding habits

This thesis examines macroevolutionary shifts on reconstructed phylogenies of two groups of insects, the Tephritoidea (true fruit flies and related families) and Plecoptera (stoneflies) using phylogenetic trees reconstructed with DNA sequence data from the small subunit ribosomal RNA and cytochrome oxidase genes. First, the Tephritoidea exhibit a variety of larval feeding habits with numerous switches from the ancestral state of saprophagy to phytophagy, parasitism, and predation within the Tephritoidea. However, there has been insufficient morphological evidence to confidently reconstruct the phylogenetic history of this group and our understanding of shifts in larval feeding habit have suffered. The molecular phylogeny is largely congruent with the morphological hypotheses, but could not resolve divergences poorly understood by morphological evidence. The results suggest that there was no progression of intermediate forms between saprophagy and the derived habits exhibited by some members of the Tephritoidea. This departure from our current understanding of macroevolutionary shifts deserves additional attention. This study lays a clear path for future investigations into this group, which will require several additional genes with phylogenetic signal at this level of divergence. Second, the Plecoptera have been used as a model for understanding how flight evolved in insects. Many of the families in this order exhibit non-flying aerodynamic locomotion, using their wings to propel themselves two-dimensionally across the water surface. The distribution of aerodynamic locomotion characters across morphological phylogenetic hypotheses was insufficient to explain the evolution of these traits. The results of this study re-rooted the topology of the previous, morphological hypotheses, with which it was otherwise largely congruent. This redefines our understanding of the phylogeny of the Plecoptera and presents a radically new hypothesis that can be explored and tested with morphological and molecular data. Because of the new rooting arrangement, the ancestral form can now be inferred to have been both flying and non-flying aerodynamic locomotion. Extant species exhibit modifications these behaviors, and many species continue to use both. This finding provides an understanding of how these behaviors evolved within the Plecoptera and give us new insight into how aerodynamic locomotion might have been an important precursor to true flight in insects.