Collaborative Research: Spatial analysis of genetic differences in salinity tolerance resulting from rapid natural selection in estuarine oysters

许多海洋动物的生命周期分为两个阶段，一个是静止的底栖成体阶段，另一个是移动的幼体阶段。水流将这些幼虫后代及其基因运送到不同的栖息地。人们认为，来自附近斑块的动物在遗传上比更接近的斑块中的动物更相似，但如果附近斑块具有不同的栖息地特征，这些遗传相似性模式可能无法维持。这个想法是我们理解适应和进化的基础，但在快速选择的影响方面还没有得到充分的检验。这项研究应用新技术来测试海洋动物的遗传特征是否会发生变化，即使具有不同环境特征的斑块之间的距离比幼虫的传播距离更近。这项研究的重点是东部牡蛎（Crassostrea virginica）在特拉华州湾，和他们的能力，以承受变化量的盐在水中。这项研究将提供新的见解的因素，控制牡蛎的生存和生长在河口不同的盐度配置文件。这三位研究人员正在与资源管理人员和利益相关者分享研究结果，以改善特拉华州湾、切萨皮克湾和纽约的贝类恢复和牡蛎种群管理。康奈尔大学的一名博士后学者和马里兰州大学的一名研究生正在该项目期间接受培训和指导。研究人员还与纽约和新泽西的教师培训项目合作，为中学生开发和传播关于牡蛎生态学的新课程材料。该项目将调查牡蛎的低盐度耐受性是否是幼虫扩散期间和定居后生存力选择的函数。基因流在河口的盐度区预计将足够高，适应性分化将不会导致达尔文的多代过程。相反，预计在每一代中的经常性生存力选择会在小的空间尺度上产生该性状的空间变异。这种反复出现的代内适应被称为表型-环境错配，并被假设产生平衡的多态性，但它从未被研究过单基因病例。该项目团队正在测试空间离散的选择模式，首先从不同的盐度区收集牡蛎，测量它们对低盐度的耐受性变化，然后使用全基因组测序测试这一特征与基因组变异之间的关联。实验性低盐度挑战使得能够在基因组比较之前/之后进行代内比较，以鉴定由于强生存力选择而改变的DNA变体。候选基因和选择性中性控制位点将在幼虫，少年，和成年人样品从相同的盐度区进行测定，以测试候选位点的变化和终身低盐度暴露之间的关联。将收集两年的环境数据，并将其添加到现有的长期数据集中，以绘制盐度变化图。所观察到的低盐度耐受性和与之相关的基因组变异的空间分布提供了一个测试，可以明确拒绝流行的假设，即所有幼虫具有相似的能力。如果幼虫不同的亲本来源的性状，差异影响他们的生存能力的浮游生物，然后表型环境的不匹配可能有深远的影响人口的连接。该项目提高了对牡蛎种群中实现的幼虫扩散和补充变异的形成机制的理解。该奖项反映了NSF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。

Many marine animals have a bipartite life cycle consisting of a stationary bottom-dwelling adult stage and a mobile larval stage. The flow of water transports these larval offspring, and their genes, to different habitat patches. It is thought that animals from nearby patches will be more genetically similar than animals in patches that are further in proximity, but these patterns of genetic similarity may not be maintained if the nearby patches have different habitat characteristics. This idea is fundamental to our understanding of adaptation and evolution, but it has not been adequately tested with respect to the effects of rapid selection. This study applies new technologies to test if the genetic signatures of marine animals change even when patches with different environmental characteristics are closer together than the dispersal distance of larvae. This research focuses on eastern oysters (Crassostrea virginica) in Delaware Bay, and their ability to withstand variability in the amount of salt in the water. This study will provide new insights on factors that control oyster survival and growth in estuaries with different salinity profiles. The three investigators are sharing study results with resource managers and stakeholders to improve shellfish restoration and oyster stock management in Delaware Bay, Chesapeake Bay, and New York. A postdoctoral scholar at Cornell and graduate student at the University of Maryland are being trained and mentored during the project. The investigators are also working with teacher training programs in New York and New Jersey to develop and disseminate new curriculum materials on oyster ecology for middle-school students.The project will investigate whether hyposalinity tolerance of oysters is a function of viability selection during larval dispersal and after settlement. Gene flow across salinity zones within an estuary is expected to be high enough that adaptive differentiation will not result from Darwinian multigenerational processes. Instead, recurrent viability selection in each generation is expected to generate spatial variation in this trait at small spatial scales. This type of recurrent within-generation adaptation has been referred to as phenotype-environment mismatches and has been hypothesized to generate balanced polymorphisms, but it has never been studied beyond single gene cases. The project team is testing for spatially discrete patterns of selection by first collecting oysters from different salinity zones, measuring variation in their tolerance to low salinity and then testing for associations between this trait and genomic variation using whole genome sequencing. Experimental hyposalinity challenges enable within-generation, before/after genomic comparisons to identify DNA variants that change as a result of strong viability selection. Candidate genes and selectively neutral control loci will be assayed in larval, juvenile, and adult samples from the same salinity zones to test for an association between variation at candidate loci and lifetime hyposalinity exposure. Two years of environmental data will be collected and added to an existing long-term data set to map salinity variation. The observed spatial distribution of hyposalinity tolerance and genomic variation associated with it provide a test that could definitively reject the prevalent assumption that all larvae have similar capabilities. If larvae differ by parental source for traits that differentially affect their viability in the plankton, then phenotype-environment mismatches can have profound consequences for population connectivity. This project improves understanding about mechanisms that shape realized larval dispersal and recruitment variation in oyster populations.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.