ANT LIA: The Role of Sex Determination in the Radiation of Antarctic Notothenioid Fish

随着南极冰盖融化和气温上升，南极动物面临着巨大的威胁。大约3400万年前，当南极洲开始降温时，大多数鱼类在当地灭绝。然而，由于防冻剂的进化，一种被称为notothenioids的物种幸存了下来。这个群体最终分裂成120多个物种。为什么这群南极鱼类进化成这么多种类？一个单一种群分裂成两个物种的一个可能原因与性基因和性染色体有关。不同的物种通常要么有不同的性别决定基因（决定个体的性腺是变成卵巢还是睾丸的基因），要么有不同的性染色体（一个物种内雄性和雌性之间不同的染色体，比如人类的X染色体和Y染色体）。我们只知道少数南极鱼的性染色体，也不知道它们性别决定的遗传基础。本研究的目的是：1)鉴定南极南极南极南极南极鱼各主要类群的性染色体；2)发现南极南极南极南极鱼各主要类群中可能的性别决定基因；3)在两组温带、温暖水域的南极鱼中发现性染色体和可能的性别决定基因。这些温暖水域的鱼类包括从未经历过寒冷的南大洋和祖先居住在后来适应温暖水域的南极海洋的鱼类。这个项目将有助于解释导致受气候变化威胁的一组物种分裂的机制。这些信息是至关重要的保护南极notothenioids的数量下降,而这些医院是主要食物来源为其他南极物种如鸟类和海豹。该项目将为不同群体的本科生提供在尤金科学中心博物馆举办永久性展览的机会。该展览将描述南极的环境，并解释其快速的气候变化。它还将介绍非洲大陆生活在水冰点以下的奇异鱼类。该项目将与该大学的科学与漫画计划以及英语系漫画研究辅修课程的学生合作，编写短篇漫画小说，解释南极生物地理、冰鱼特色以及该项目的科学进展。随着南极洲变冷，大多数物种从这片大陆的水域中消失了，但冰鱼却进化成了一个物种群。是什么促成了这种辐射？Coyne的“物种形成的两条规则”为物种分化提供了解释：1)种间杂交的不正常性别是指具有两种不同性染色体的性别（即，在人类中，它将是XY个雄性而不是XX个雌性）；2)“性染色体在物种形成中起着巨大的作用”。这些想法推动了该项目的主要假设：新的性染色体和新的性别决定基因与类冷冻鱼物种形成事件有关。本研究的主要目的是鉴定许多南极鱼物种的性染色体和候选性别决定基因。该项目的第一个目标是确定南极鱼类的性染色体，并提出这样一个问题：新的性染色体是否伴随着物种形成事件？知识空白包括：哪些物种有隐性染色体；它们有新进化的性染色体；染色体为XX/XY或ZZ/ZW。方法采用种群基因组学（RAD-seq和Pool-seq）对20多种南极冷冻鱼进行分析。预测是性染色体的频繁更替。该项目的第二个目标是确定候选的南极冷冻鱼性别决定基因，并提出以下问题：新的性别决定基因是否伴随着南极冷冻鱼物种形成事件？一个知识缺口是任何南极鱼性别决定基因的身份。初步数据表明，三个性别连锁位点位于或邻近三个不同的候选性别决定基因：1)黑鳍鱼的bmpr1ba重复基因；2)南乔治亚冰鱼gsdf的串联重复；3)条带体中GSDF的转置副本。方法包括对候选性基因异常的冷冻鱼性连锁位点的基因组邻域进行注释，对性染色体进行测序，并通过CRISPR诱变技术检测斑马鱼的性基因变异。预测是性别决定基因的频繁更替。该项目的第三个目标是鉴定温带南极鱼的性染色体和性别决定基因。基部分化的温带notothenioids （‘ basals ‘）缺乏可识别的性染色体，与温度提示的性别决定一致，并且一个’基部’物种是雌雄同体。持续寒冷的南大洋排除了温度的影响，而温度是许多温带鱼类常见的性别决定因素，有利于基因性别决定。一些冰鱼重新侵入温带水域（“海归”）。知识空白包括海归和海归是否有很强的性别决定基因。方法采用pool-seq。据预测，基岩企鹅的基因性别决定能力较弱，海归企鹅与它们在南极的姐妹进化支具有相同的、但较弱的性别连锁位点。将在尤金科学中心博物馆建立一个永久性展览，暂定名为：南极：鱼类和气候变化。成千上万的游客，尤其是学生，将接触到南极生态系统的科学和气候变化的影响。研究小组将与该大学的科学和漫画计划合作，制作短篇漫画小说，解释南极生物地理、冰鱼特色和这个项目。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Antarctic animals face tremendous threats as Antarctic ice sheets melt and temperatures rise. About 34 million years ago, when Antarctica began to cool, most species of fish became locally extinct. A group called the notothenioids, however, survived due to the evolution of antifreeze. The group eventually split into over 120 species. Why did this group of Antarctic fishes evolve into so many species? One possible reason why a single population splits into two species relates to sex genes and sex chromosomes. Diverging species often have either different sex determining genes (genes that specify whether an individual’s gonads become ovaries or testes) or have different sex chromosomes (chromosomes that differ between males and females within a species, like the human X and Y chromosomes). We know the sex chromosomes of only a few notothenioid species and know the genetic basis for sex determination in none of them. The aims of this research are to: 1) identify sex chromosomes in species representing every major group of Antarctic notothenioid fish; 2) discover possible sex determining genes in every major group of Antarctic notothenioid fish; and 3) find sex chromosomes and possible sex determining genes in two groups of temperate, warmer water, notothenioid fish. These warmer water fish include groups that never experienced the frigid Southern Ocean and groups that had ancestors inhabiting Antarctic oceans that later adjusted to warmer waters. This project will help explain the mechanisms that led to the division of a group of species threatened by climate change. This information is critical to conserve declining populations of Antarctic notothenioids, which are major food sources for other Antarctic species such as bird and seals. The project will offer a diverse group of undergraduates the opportunity to develop a permanent exhibit at the Eugene Science Center Museum. The exhibit will describe the Antarctic environment and explain its rapid climate change. It will also introduce the continent’s bizarre fishes that live below the freezing point of water. The project will collaborate with the university’s Science and Comics Initiative and students in the English Department’s Comics Studies Minor to prepare short graphic novels explaining Antarctic biogeography, icefish specialties, and the science of this project as it develops. As Antarctica cooled, most species disappeared from the continent’s waters, but cryonotothenioid fish radiated into a species flock. What facilitated this radiation? Coyne’s “two rules of speciation” offer explanations for why species diverge: 1) the dysgenic sex in an interspecies hybrid is the one with two different sex chromosomes (i.e., in humans, it would be XY males and not XX females); and 2) “sex chromosomes play an outsized role in speciation”. These ideas propel the project’s main hypothesis: new sex chromosomes and new sex determination genes associate with cryonotothenioid speciation events. The main objective of the research is to identify notothenioid sex chromosomes and candidate sex-determination genes in many notothenioid species.The project’s first aim is to identify Antarctic fish sex chromosomes, asking the question: Did new sex chromosomes accompany speciation events? Knowledge gaps include: which species have cryptic sex chromosomes; which have newly evolved sex chromosomes; and which are chromosomally XX/XY or ZZ/ZW. Methods involve population genomics (RAD-seq and Pool-seq) for more than 20 Antarctic cryonotothenioids. The prediction is frequent turnover of sex chromosomes. The project’s second aim is to Identify candidate Antarctic cryonotothenioid sex-determination genes, asking the question: Did new sex-determination genes accompany Antarctic cryonotothenioid speciation events? A knowledge gap is the identity of sex determination genes in any notothenioid. Preliminary data show that three sex-linked loci are in or adjacent to three different candidate sex determination genes: 1) a duplicate of bmpr1ba in blackfin icefish; 2) a tandem duplicate of gsdf in South Georgia icefish; and 3) a transposed duplicate of gsdf in striped notothen. Methods involve annotating the genomic neighborhoods of cryonotothenioid sex linked loci for anomalies in candidate sex genes, sequencing sex chromosomes, and testing sex gene variants by CRISPR mutagenesis in zebrafish. The prediction is frequent turnover of sex determination genes. The project’s third aim is to identify sex chromosomes and sex-determination genes in temperate notothenioids. Basally diverging temperate notothenioids (‘basals’) lack identifiable sex chromosomes, consistent with temperature-cued sex determination, and one ‘basal’ species is a hermaphrodite. The constantly cold Southern Ocean rules out temperature, a common sex determination cue in many temperate fish, favoring genetic sex determination. Some cryonotothenioids re-invaded temperate waters (‘returnees’). Knowledge gaps include whether basals and returnees have strong sex determination genes. Methods employ pool-seq. The prediction is that genetic sex determination is weak in basals and that returnees have the same, but weaker, sex-linked loci as their Antarctic sister clade. A permanent exhibit will be established at the Eugene Science Center Museum tentatively entitled: The Antarctic: its fishes and climate change. Thousands of visitors, especially school children will be exposed, to the science of Antarctic ecosystems and the impacts of climate change. The research team will collaborate with the university’s Science and Comics Initiative to produce short graphic novels explaining Antarctic biogeography, icefish specialties, and this project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.