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

非技术性摘要本研究主要针对寄生在介壳虫上的真菌七星天牛的生物学进行研究。介壳虫是常见的农业和园艺害虫，七倍体是一种能使其感染的昆虫灭菌的真菌。然而，七星菌落需要感染和未感染的昆虫才能生存。由于七星天牛生活在寄主介壳虫的复杂关系中，其多样性与寄主介壳昆虫的多样性和多样性密切相关。本研究试图阐明寄主和寄生虫的任何相关的多样性模式，并确定导致这些模式形成的过程。提出的研究有两个主要部分。第一部分使用真菌和寄主昆虫的DNA序列数据来检查寄主联合和共种的大规模模式，这些模式构成了共生环境中的多样性。系统发育学方法被用来推断宿主和寄生虫的历史，并将重建的历史进行比较，以确定宿主进化如何与寄生虫进化有关。第二部分实施了分析来自美国东南部多个七星生物种群的DNA序列数据的方法，以识别产生大规模模式的过程。宿主和寄生虫的种群过程，如迁移和扩散，都是从DNA序列变化中分别和同时估计的。将来自不同寄主昆虫和生态环境但地理范围重叠的几个不同真菌物种的这些过程进行比较，将确定宿主和寄生虫种群过程相互影响的程度。这两个主要部分的结合提供了对这种共生关系中进化多样性的洞察，并代表了第一个应用关键遗传学方法来理解这种经典真菌/昆虫关系的生态和进化的研究。这项研究在几个具体方面使公众受益。这项研究通过淀粉学学生和昆虫学家专家的合作来促进跨学科交流。这项研究也为本科生提供了获得研究经验的机会。最后，这项研究加深了对真菌/鳞片害虫寄生可能导致植物害虫生物防治的理解。

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.