Systematics and Biogeography of the Sawfly Genus Pristiphora Latreille (Hymenoptera: Tenthredinidae) in North America

Sawflies in the subfamily Nematinae (Hymenoptera: Tenthredinidae) are cold-adapted insects that reach their greatest species richness in temperate, boreal, and arctic/subarctic regions of the Northern Hemisphere – a pattern that runs counter to that of most other organisms. The reasons for this pattern remain unclear, just as the full extent of the subfamily’s diversity remains unknown. This dissertation addresses these gaps in knowledge in the genus Pristiphora Latreille: first, by revising the Nearctic representatives of three species groups: the Pristiphora litura group, P. ruficornis group, and P. rufipes group (23 species out of 57 total known from the Nearctic); second, by inferring a molecular phylogeny for the genus using DNA sequence data from one mitochondrial and three nuclear loci – obtained from specimens from across the Holarctic region – which is subsequently used to reconstruct the genus’ biogeographic history; and third, by investigating the recent phylogeographic history of the common and widespread Holarctic species Pristiphora cincta Newman. In this dissertation, thorough descriptions and diagnoses are provided for all Nearctic species, two species are newly described, four new synonymies are proposed, and two formerly Palaearctic species are newly reported for the Nearctic. The genus boundaries of Pristiphora are discussed in light of new morphological and molecular evidence. Biogeographic reconstructions suggest a relatively recent radiation within the most speciose groups of Pristiphora, corresponding to the establishment of cool-temperate, boreal, and arctic/subarctic biotas across the northern hemisphere, beginning in the later half of the Miocene (ca. 15 Ma). Ancestral range reconstructions also indicate numerous geodispersals between the Palaearctic and Nearctic over the last ca. 110 million years. Finally, phylogeographic results suggest that climatic cycles during the Pleistocene led to the diversification of lineages within P. cincta, populations of which may have survived glaciations in numerous isolated refugia, including in remote parts of the High Arctic. Taken together, the results suggest a complex and rich biogeographic history for the genus throughout the northern hemisphere. Important progress is made towards understanding the evolutionary history, biogeography, and taxonomy of the genus Pristiphora – and thereby of sawflies and northern hemisphere biogeography more broadly.