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，当南极洲开始变冷时，大多数鱼类物种在当地灭绝了。然而，由于防冻剂的进化，一种名为notothenioid的物种幸存了下来。这个群体最终分成了120多个物种。为什么这群南极鱼类进化成了这么多物种？一个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(决定一个人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(同一物种中雌雄不同的染色体，比如人类的X和Y染色体)。我们只知道为数不多的无尾类物种的性染色体，也不知道它们中任何一个物种性别决定的遗传基础。本研究的目的是：1)确定代表南极所有主要鱼类种群的性染色体；2)在南极所有主要种群中发现可能的性别决定基因；3)在温带、温暖水域的两个种群中发现性染色体和可能的性别决定基因。这些较温暖的水域鱼类包括从未经历过寒冷的南大洋的群体，以及有祖先居住在南极海洋的群体，这些群体后来适应了较温暖的水域。该项目将有助于解释导致一组受到气候变化威胁的物种分化的机制。这一信息对于保护南极拟脊椎动物数量的减少至关重要，后者是鸟类和海豹等其他南极物种的主要食物来源。该项目将为不同的本科生群体提供在尤金科学中心博物馆开发永久展览的机会。展览将描述南极环境，并解释其快速的气候变化。它还将介绍生活在冰点以下的非洲大陆奇怪的鱼类。该项目将与该大学的科学与漫画倡议和英语系漫画研究辅修专业的学生合作，编写短篇漫画小说，解释南极生物地理学、冰鱼特产以及该项目发展过程中的科学。随着南极洲的降温，大多数物种从该大陆的水域中消失了，但冷冻鱼却辐射成了一个物种群。是什么促成了这种辐射？科因的“物种形成的两条规则”解释了物种分化的原因：1)物种间杂交中的不育性别是具有两条不同性染色体的性别(即，在人类中，它将是XY男性而不是XX女性)；2)“性染色体在物种形成中扮演着非常重要的角色”。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冷核类固醇物种形成事件有关。这项研究的主要目的是在许多诺氏类物种中识别诺氏类性染色体和候选性别决定基因。该项目的第一个目标是识别南极鱼类的性染色体，提出一个问题：新的性染色体是否伴随着物种形成事件？知识差距包括：哪些物种具有隐蔽的性染色体；哪些物种具有新进化的性染色体；以及哪些物种在染色体上属于XX/XY或ZZ/ZW。方法包括对20多个南极冷冻菌进行种群基因组学(RAD-SEQ和Pool-SEQ)。预测是性染色体的频繁更替。该项目的第二个目标是确定南极冷杉类性别决定基因的候选，提出一个问题：新的性别决定基因是否伴随着南极冷杉类物种形成事件？知识鸿沟指的是性别决定基因在任何一种类天牛中的同一性。初步数据表明，三个性别连锁基因位于或邻近三个不同的候选性别决定基因：1)黑鳍银鱼中bmpr1ba的重复；2)南乔治亚州银鱼中GSDF的串联重复；以及3)条纹银鱼中GSDF的转位重复。方法包括注释冷冻性连锁基因的基因组邻域以寻找候选性基因中的异常，对性染色体进行测序，并通过CRISPR突变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在温带海鞘中识别性染色体和性别决定基因。从基本上说，温带脊椎动物(‘基端’)缺乏可识别的性染色体，这与温度决定性别的决定是一致的，一个‘基端’种是两性的。持续寒冷的南大洋排除了温度，这在许多温带鱼类中是一种常见的性别决定信号，有利于遗传性别决定。一些低温类固醇重新入侵温带水域(‘返回者’)。知识差距包括基地和归国人员是否具有很强的性别决定基因。方法采用池序法。预测是，遗传性别决定在基岩中很弱，海归与他们在南极的姐妹支系具有相同但更弱的性别连锁基因。尤金科学中心博物馆将设立一个永久展览，暂时命名为：南极：它的鱼类和气候变化。数以千计的游客，特别是小学生，将接触到南极生态系统的科学和气候变化的影响。研究团队将与该大学的科学和漫画倡议合作，制作短篇漫画小说，解释南极生物地理学、冰鱼特产和这个项目。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.