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

摘要本文主要研究了寄生于蚧虫体内的真菌九隔担子菌的生物学特性。介壳虫是常见的农业和园艺害虫，而七孢子虫是一种真菌，它可以使被它感染的昆虫绝育。然而，七孢子菌的菌落需要感染和未感染的昆虫才能生存。由于孢子菌与寄主蚧虫生活在这种复杂的关联中，因此其多样性可能与寄主蚧虫的多样性和多样化密切相关。本研究旨在阐明宿主和寄生虫中任何相关的多样化模式，并确定导致这些模式形成的过程。本研究主要分为两个部分。第一部分使用来自真菌和寄主昆虫的DNA序列数据来检查寄主结合和共种的大规模模式，这些模式在共生中构成了多样性。系统发育学方法用于推断宿主和寄生虫的历史，并将这些构建的历史进行比较，以确定宿主进化与寄生虫进化之间的关系。第二部分实现了分析来自美国东南部多个septobasidium物种种群的DNA序列数据的方法，以确定产生大规模模式的过程。从宿主和寄生虫的DNA序列变化分别和同时估计迁移和扩散等种群过程。比较几种不同真菌种类的这些过程，它们具有不同的寄主昆虫和生态，但在重叠的地理范围内，将确定寄主和寄生虫种群过程相互影响的程度。结合这两个主要部分提供了对这种共生关系的进化多样化的见解，并代表了第一个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进化的研究。这项研究在几个具体方面对公众有益。本研究通过淀粉学学生和一位昆虫专家的合作，促进了跨学科的交流。这项研究还为本科生提供了获得研究经验的机会。最后，该研究进一步加深了对真菌/鳞片昆虫寄生的认识，为植物害虫的生物防治提供了可能。

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.