This research focuses on the biology of Septobasidium, a fungal parasite on scale insects. Scale insects are common agricultural and horticultural pests, and Septobasidium is a fungus that sterilizes the insects that it infects. However, colonies of Septobasidium require both infected and uninfected insects to survive. Because Septobasidium lives in this complex association with its host scale insects its diversification is expected to be tightly linked to diversity and diversification in host scale insects. This research seeks to elucidate any correlative patterns of diversification in the hosts and parasites and to determine the processes that lead to the formation of those patterns. The proposed research has two main parts. The first part uses DNA sequence data from both fungi and host insects to examine large-scale patterns of host association and cospeciation that structure diversity within the symbiosis. Phylogenetic methods are used to infer the history of hosts and parasites, and these reconstructed histories are compared to determine how host evolution is related to parasite evolution. The second part implements methods to analyze DNA sequence data from multiple populations of Septobasidium species from across the southeastern United States in order to identify processes that generate the large-scale patterns. Population processes such as migration and dispersal are estimated from DNA sequence variation separately and simultaneously for both hosts and parasites. Comparing these processes from several different fungal species with different host insects and ecologies but from overlapping geographic ranges will determine how strongly the host and parasite population processes influence each other. Combining the two major parts provides insight into evolutionary diversification in this symbiosis and represents the first study to apply critical genetic approaches to understand the ecology and evolution of this classic fungus/ insect relationship. This study benefits the public in several specific ways. This study improves cross discipline communication through collaboration of a mycology student and an expert entomologist. The study also provides opportunities for undergraduate students to gain research experience. Finally, the research furthers understanding of fungal/ scale insect parasitism that may lead to biological control of plant pests.
