DISSERTATION RESEARCH: Coevolutionary Diversification in Septobasidium, a Fungal Symbiont of Scale Insects

非技术摘要本研究的重点是寄生在介壳虫上的真菌隔担子的生物学。介壳虫是常见的农业和园艺害虫，隔担子是一种真菌，它可以使感染的昆虫绝育。然而，隔担子的菌落需要感染和未感染的昆虫才能生存。由于隔担子与寄主蚧虫的关系复杂，其多样性与寄主蚧虫的多样性密切相关，本研究旨在阐明寄主和寄生虫多样性的相关模式，并确定导致这些模式形成的过程.本研究主要包括两个部分。第一部分使用真菌和寄主昆虫的DNA序列数据来研究共生体中结构多样性的寄主联合和物种形成的大规模模式。系统发生学方法被用来推断宿主和寄生虫的历史，并将这些重建的历史进行比较，以确定宿主进化与寄生虫进化之间的关系。第二部分实施的方法来分析DNA序列数据从多个群体的Septobasidium物种从整个美国东南部，以identifyprocesses产生的大规模模式。根据宿主和寄生虫的DNA序列变异分别和同时估计种群的迁移和扩散过程。比较这些过程从几个不同的真菌物种与不同的寄主昆虫和生态，但从重叠的地理范围将确定如何强烈的主机和寄生虫种群过程相互影响。结合这两个主要部分提供了对这种共生关系中进化多样性的深入了解，并代表了第一项应用关键遗传方法来理解这种经典真菌/昆虫关系的生态学和演变的研究。这项研究通过真菌学学生和昆虫学家专家的合作提高了跨学科的交流。本研究还为本科生提供了获得研究经验的机会。最后，本研究进一步加深了对真菌/蚧虫寄生的理解，这可能导致植物害虫的生物防治。

Nontechnical AbstractThis research focuses on the biology of Septobasidium, a fungal parasiteon scale insects. Scale insects are common agricultural and horticulturalpests, and Septobasidium is a fungus that sterilizes the insects that itinfects. However, colonies of Septobasidium require both infected anduninfected insects to survive. Because Septobasidium lives in this complexassociation with its host scale insects its diversification is expected tobe tightly linked to diversity and diversification in host scale insects.This research seeks to elucidate any correlative patterns ofdiversification in the hosts and parasites and to determine the processesthat lead to the formation of those patterns. The proposed research hastwo main parts. The first part uses DNA sequence data from both fungi andhost insects to examine large-scale patterns of host association andcospeciation that structure diversity within the symbiosis. Phylogeneticmethods are used to infer the history of hosts and parasites, and thesereconstructed histories are compared to determine how host evolution isrelated to parasite evolution. The second part implements methods toanalyze DNA sequence data from multiple populations of Septobasidiumspecies from across the southeastern United States in order to identifyprocesses that generate the large-scale patterns. Population processessuch as migration and dispersal are estimated from DNA sequence variationseparately and simultaneously for both hosts and parasites. Comparingthese processes from several different fungal species with different hostinsects and ecologies but from overlapping geographic ranges willdetermine how strongly the host and parasite population processesinfluence each other. Combining the two major parts provides insight intoevolutionary diversification in this symbiosis and represents the firststudy to apply critical genetic approaches to understand the ecology andevolution of this classic fungus/ insect relationship.This study benefits the public in several specific ways. This studyimproves cross discipline communication through collaboration of amycology student and an expert entomologist. The study also providesopportunities for undergraduate students to gain research experience.Finally, the research furthers understanding of fungal/ scale insectparasitism that may lead to biological control of plant pests.