What are the fitness and evolutionary consequences of the Y chromosome?

男性(Y)染色体存在的适应性解释与个体适应性的增强、近亲繁殖的减少和/或性选择的增强相结合。由于这两种过程的结果都是适应度的增加，因此迄今为止，很难从经验上区分它们。测试Y染色体在这两个重要进化过程中相对重要性的实验证据很少（如果不是没有的话，在最近的文献检索中），因为很难找到能够产生男性表型和配子而不拥有Y染色体的雌雄异株生物。大麻是一种雌雄异株植物，性别由XY系统决定；然而，这个物种的性别表达对环境非常敏感。因此，大麻中的性染色体和性表达可以解耦：1)植物可以拥有XY染色体补体，但产生雄性或雌性花；2)植物可以拥有XX染色体补体，但产生雄性或雌性花。这种植物为检验关于Y染色体在性分化和表达、性选择和避免近亲交配中的作用的基本假设提供了一个很好的平台。我的研究计划的长期目标是发现驱动进化的原理，这是人口统计学的结果，尤其是交配过程。我们处于一个独特的位置，可以使用具有灵活性表达的植物来测试关于染色体互补和交配的基本问题。从这种植物中获得的见解可转移到其他雌雄异株植物（包括芦笋、芦笋和啤酒花）。我的研究计划将通过探索：遗传和环境因素如何影响大麻的生殖生物学：a)数量性状的性别特异性遗传力；b)性别表达的变化；灵活的性别表达对以下方面的影响：a)生活史和繁殖力；b)配子和胚胎的遗传组成；以及Y染色体在减少近亲繁殖或增加性选择方面的相对重要性。这个研究项目将使我们最终能够在保持雌雄异株系统的同时，将性过程与性染色体分离开来，并使我们能够评估Y染色体在交配和性选择中的作用。此外，这项研究将培养学生的多样性技能，包括生态和群体遗传学，以及蛋白质生物化学。

Adaptive explanations of the existence of male (Y) chromosomes have been coupled to increased individual fitness with reduced inbreeding and/or stronger sexual selection. Because the outcome of the two processes is increased fitness, it has, thus far, proved difficult to discriminate among them empirically. Experimental evidence to test the relative importance of Y chromosomes in these two important evolutionary processes is rare (if not absent, in a recent literature search) because it is also difficult to find dioecious organisms that can produce male phenotypes and gametes without also possessing the Y chromosome. Cannabis sativa is a dioecious plant with sex determined by an XY system; however, sex expression in this species is sensitive to environmental context. Thus, sex chromosomes and sex expression in cannabis can be decoupled: 1) plants can possess XY chromosome complements but produce either male or female flowers, or 2) they can possess XX chromosome complements but produce either male or female flowers. This plant provides an excellent platform to test basic hypotheses about the role of the Y chromosome in sexual differentiation and expression, sexual selection and inbreeding avoidance. The long-term objective of my research program is to discover principles that drive evolution as a consequence of demography, especially mating processes. We are in a unique position to test basic questions about chromosome complement and mating using a plant with flexible sex expression. Insights gleaned from this plant are transferrable to other dioecious plants (including Asparagus, Rumex, and hops). My research program will study the reproductive biology of cannabis by exploring: how genetic and environmental factors influence a) sex-specific heritability of quantitative traits, and b) shifts in sex expression; the consequences of flexible sex expression for: a) life history and fecundity, and b) the genetic composition of gametes and embryos; and the relative importance of Y chromosomes in reducing inbreeding or increasing sexual selection.This research program will allow us to finally separate the process of sex from sex chromosomes while still maintaining a dioecious system, and allow us to assess the role of the Y chromosome in mating and sexual selection. Furthermore, this research will train students in a diversity of skillsets, including ecological and population genetics, and protein biochemistry.