PINE, APHIDS, AND PARASITOID WASPS: PATTERNS OF COSPECIATION AND HOST SWITCHES IN A TRI-TROPHIC SYSTEM

Bass, Amber

ABSTRACT: Ecological interactions may drive speciation events, and the processes that drive these speciation events can leave behind patterns in the phylogenies of interacting taxa. These patterns have been studied extensively in herbivores and host plants, as well as parasites and their hosts, but rarely in tri-trophic systems. Here, we examine three closely related groups of interacting taxa, including parasitoid wasps (Pauesia), aphid herbivores (Cinara), and pine trees (Pinus) to determine if the patterns between each interacting taxa indicate that cospeciation or host switches are more dominant. We create phylogenies of Cinara and Pauesia in the southeastern United States using ddRADseq data and analyze publicly available data for Pinus. Most Cinara and Pauesia were specialized, with no species utilizing more than three hosts, indicating that this system is well suited to cophylogenetic study, and host interactions likely play a role in the speciation of these taxa. Pauesia was slightly more specialized on Pinus, suggesting phytochemistry may constrain the host breadth of these wasps and lead to coevolutionary patterns between Pauesia and Pinus. Distance-based cophylogenetic analyses suggest that all three interacting pairs of taxa were significantly congruent, and the majority of links between terminal taxa support these findings across each of the paired phylogenies. However, event-based methods show that cospeciation events and host switches were present in nearly equal proportions, and duplications and sorting events occurred at a lower frequency if at all. These analyses demonstrated at least one lineage with cascading speciation, however the underlying mechanisms require population level analyses. Both Cinara and Pauesia require revisions and the development of updated taxonomic resources for identification. This system presents an ideal model group to study coevolutionary patterns and multi-trophic community dynamics across macro- and microevolutionary time scales.