Collaborative Research: Does sexual selection promote speciation and extinction? A test with Late Cretaceous Ostracoda from the US Gulf Coastal Plain

摘要了解控制生物多样性起源和灭绝的因素是进化生物学的中心目标，与当今地球生物多样性的保护和管理直接相关。最近的研究表明，物种形成（即新物种的进化）和灭绝可能受到性选择的影响，这是一种个体为获得配偶而相互竞争的过程。迄今为止，对这一假说的检验还没有检验实际的物种形成和灭绝事件，而是依赖于代用物，比如现代物种的保护状况。在这里，研究人员利用被称为介形虫的小型甲壳类动物的丰富化石记录，测试了性选择对物种形成和灭绝的影响。这些动物是不寻常的，因为它们的性别可以从它们的壳中确定，即使是化石，研究人员可以利用雄性和雌性在壳形状和大小上的差异程度来衡量性选择的强度。在这项研究中，研究人员将把介形虫物种的性选择强度与物种形成和灭绝的模式联系起来，这些样本跨越了8500万到6000万年前的一段时间，沿着美国东南部从德克萨斯州到佐治亚州的一条狭长地带，在这段时间内处于海底。除了本研究的科学目标外，研究人员还将以教师和学者的身份指导一名博士后科学家，并让多名本科生参与该项目。研究人员还将为史密森尼自然历史博物馆开展几项公共教育活动。理解物种灭绝和起源背后的机制是宏观进化理论的核心，有助于解释生命的多样性和历史。最近的经验证据和理论模型表明，性选择，一种自然选择的形式，作用于交配成功的变化，可以驱动物种形成和灭绝。迄今为止，性选择与物种灭绝或物种形成之间关系的测试严重依赖于新学数据，并使用实际宏观进化事件的弱代理，如保护状态（灭绝）或进化支系丰富度（物种形成）。在这里，该项目利用丰富的介形类化石记录，并提议对两性二态性（一种表明性选择强度的指标）是否与实际灭绝和物种形成的不同速度有关进行首次检验。该研究首次验证了“性选择与物种形成和灭绝正相关”这一宏观进化假说，重点研究了美国墨西哥湾沿岸平原（GCP）保存完好的白垩纪晚期至古新世介形虫的样本记录。具体来说，该项目将：(1)测量两性异形的大小？性别选择的代表？使用基于轮廓的形态计量学；(2)记录了晚白垩世和早古新世经分类审查的介形虫种的地层范围；(3)利用基于似然的模型拟合检验两性二态性对物种起源或灭绝倾向的影响。

Nontechnical AbstractUnderstanding the factors that control the origin and extinction of biodiversity is a central goal of evolutionary biology and is directly relevant to the conservation and management of biodiversity on the Earth today. Recent research suggests that speciation (i.e., the evolution of new species) and extinction can be affected by sexual selection, a process that occurs when individuals compete with each other for access to mates. To date, tests of this hypothesis have not examined actual speciation and extinction events, relying instead on proxies, such as the conservation status of modern species. Here the researchers test the effects of sexual selection on speciation and extinction using the rich fossil record of tiny crustaceans called ostracodes. These animals are unusual because their sex can be determined from their shells, even as fossils, and the researchers can use the extent to which males and females differ in shell shape and size as a measure of the intensity of sexual selection. In this research, the researchers will relate the strength of sexual selection in ostracode species to patterns of speciation and extinction in samples that span a time interval from 85 to 60 million years ago along a swath of the southeastern United States from Texas to Georgia that was under the sea during this time period. In addition to the scientific goals of this research, the researchers will mentor a post-doctoral scientist as both a teacher and scholar, and involve multiple undergraduate students in the project. The researchers will also develop several public education activities for the Smithsonian Museum of Natural History.Technical DescriptionUnderstanding the mechanisms that underlie species extinction and origination is central to macroevolutionary theory and helps to explain the diversity and history of life. Recent empirical evidence and theoretical models suggest that sexual selection, a form of natural selection that acts upon variation in mating success, can drive both speciation and extinction. To date, tests of the association of sexual selection with either extinction or speciation have relied heavily on neontological data and use weak proxies of actual macroevolutionary events, such as conservation status (for extinction) or clade richness (for speciation). Here the project capitalize on the rich fossil record of ostracodes and propose to perform the first examination of whether sexual dimorphism, an indicator of the strength of sexual selection, is associated with differential rates of actual extinction and speciation.The research provides the first test of the macroevolutionary hypothesis that sexual selection is positively association with both speciation and extinction, focusing on the well-preserved and well-sampled record of Late Cretaceous through Paleocene ostracodes on the US Gulf Coastal Plain (GCP). Specifically, the project will: (1) measure the magnitude of sexual dimorphism?a proxy for sexual selection?using outline-based morphometrics; (2) document the stratigraphic ranges of taxonomically vetted ostracode species from the Late Cretaceous and early Paleocene; (3) test, using likelihood-based model fitting, the influence of sexual dimorphism on the propensity of species to originate or go extinct.