DISSERTATION RESEARCH: The evolution of symbiotic polydnaviruses in Parapanteles parasitoid wasps

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When two different species have a long-term and consistent interaction they reciprocally influence each other's evolutionary fate. Understanding how these interactions with other species have shaped an organism over time is key to understanding how and why that organism is the way it is today, which is fundamentally important to understanding the complexity and diversity of nature and very useful when trying to control an organism with an economic consequence. Many types of wasps inject their eggs into the body of another living insect, which hatch into larvae that consume the host. Wasps in the subfamily Microgastrinae (Hymenoptera: Braconidae) use a specialized virus, polydnavirus, to prevent their hosts, caterpillars, from destroying their eggs and larvae. Microgastrine wasps are one of the most important ecological and agricultural natural enemies to the caterpillars of butterflies and moths, including many agricultural pests. This research will compare the genomes polydnaviruses from a small group of closely related microgastrines. This group of microgastrines was at one point a single species that attacked 1-3 species of host caterpillars, but evolved over time into about 20 species that each attack different caterpillar species. The goal of this project is to identify which virus genes changed the most and which changed the least as this group of wasps evolved into several different species which have adapted to different hosts. This will identify which virus genes have universally important functions for disabling caterpillars' immune defenses and which genes may have specific functions that are adapted to work in a specific host. This will contribute to understanding how polydnaviruses help microgastrines adapt to new host caterpillars, how they are able to adapt to thousands of different caterpillar immune systems, and why there are so many species of microgastrines. This is especially important for understanding why some groups of organisms evolve into many more species than other groups of organisms, and for discovering new ways to control caterpillar species, many of which are important agricultural pests.Polydnavirus genes that interfere with host immunity are hypothesized to evolve rapidly in an evolutionary arms-race with the host immune adaptations. Polydnavirus genomes are integrated into the microgastrine wasps' nuclear genome. Parapanteles Ashmead is a small microgastrine genus with well-studied microgastrine host use patterns. A draft genome of Parapanteles continua has already been sequenced and assembled and putative polydnavirus genes have been identified within it. This research will sequence and assemble the genomes of 20 more Parapanteles species, annotate their polydnavirus genes, and phylogenetically investigate how these genes have evolved, especially in relation to host-switches.