Hybridization, sex determination, and evolutionary diversification in freshwater fishes

当亲缘关系密切的物种产生后代时，杂交一直是进化多样化的组成部分，并深深地交织在许多动植物谱系的进化史中。虽然杂交可以通过为新物种的快速形成提供原料和促进新性状来促进进化多样性，但杂交也可以通过同质化新分化的谱系来抑制多样性。我的研究重点是描述进化过程，特别是杂交过程，如何影响生物多样性的进化和维持。一个相对未被探索的领域是准确描述主要的基因组重排，包括性别决定机制的进化更替，如何影响杂交结果。基因组的性别决定区域被认为在新物种的进化和维持新生物种之间的生殖隔离方面至关重要，但我们对性别决定的遗传机制的了解在许多分类群中仍然不完整，包括鱼类。FISH的性别决定机制非常不同，包括具有分化的性染色体的遗传性别决定，没有分化的性染色体(包括多基因系统)的遗传性别决定，两性个体和环境性别决定。众所周知，鱼类的性别决定系统在密切相关的鱼类群体中是不同的，甚至在一个物种内的不同种群之间也是如此。我推测，性别决定机制决定了北美两类淡水鱼的杂交结果，特别是卡口鱼和银鱼。这两个进化谱系都受到了杂交的影响，但方式截然不同。卡口吸虫是一个物种丰富、表型多样、地理分布广泛的科(卡口科)的一部分，该科起源于大约5000万年前的异源四倍体杂交祖先，现存的卡口科物种进行了广泛的杂交。与之形成鲜明对比的是，在大约5万年前的一次杂交事件中，嗜铬鱼和新生对虾之间的杂交事件呈现出了截然不同的结果，即雌核发育的起源，这是一种罕见的现象，即单性和无性杂交血统进行克隆繁殖。我将使用基因组数据来描述卡口目和铬属物种性别决定的遗传基础，并确定遗传性别决定机制如何塑造这些谱系中历史和当代杂交的结果。通过明确地将性别决定与这两个谱系的杂交结果联系起来，我将促进我们对性别决定基因如何更广泛地牵涉到进化多样性和维持生物多样性的理解。

Hybridization, when closely related species produce offspring, has been an integral part of evolutionary diversification, and is deeply entwined in the evolutionary history of many lineages of plants and animals. While hybridization can promote evolutionary diversification through providing raw material for the rapid formation of new species and promoting novel traits, hybridization can also inhibit diversification by homogenizing newly differentiated lineages. My research focuses on describing how evolutionary processes, specifically hybridization, influence the evolution and maintenance of biodiversity. One relatively unexplored area is describing exactly how major genomic rearrangements, including evolutionary turnover in sex determination mechanisms, influences hybridization outcomes. Sex determining regions of the genome are believed to have been crucially important in the evolution of new species and maintenance of reproductive isolation between nascent species, but our understanding of genetic mechanisms of sex determination is still incomplete in many taxa, including fish. Fish have extremely variable sex determination mechanisms that include genetic sex determination with differentiated sex chromosomes, genetic sex determination without differentiated sex chromosomes (including polygenic systems), individuals that are hermaphrodites, and environmental sex determination. Sex determination systems in fish are known to differ within closely related groups of fish, and even across populations within a species. I hypothesize that sex determination mechanisms have shaped outcomes of hybridization in two groups of freshwater fishes in North America, specifically Catostomus suckers and Chrosomus dace. Both of these evolutionary lineages have been influenced by hybridization, but in very different ways. Catostomus suckers are part of a species-rich, phenotypically diverse, and geographically widespread family (Catostomidae) that arose from an allotetraploid hybrid ancestor approximately 50 million years ago, and extant Catostomus species hybridize extensively. In contrast, Chrosomus dace present a much different outcome of a hybridization event believed to have occurred between C. eos and C. neogaeus approximately 50,000 years ago, namely the origin of gynogenesis, a rare phenomenon where unisexual, asexual hybrid lineages reproduce clonally. I will use genomic data to describe the genetic basis of sex determination for both Catostomus and Chrosomus species, and identify how genetic sex determination mechanisms have shaped outcomes of both historical and contemporary hybridization in these lineages. By explicitly linking sex determination with hybridization outcomes for these two lineages, I will advance our understanding of how sex-determining loci might be more broadly implicated in evolutionary diversification and the maintenance of biodiversity.