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

许多海洋动物的生活史由固定的底栖成虫阶段和活动的幼虫阶段组成。水流将这些幼虫的后代及其基因输送到不同的栖息地。人们认为，来自附近斑块的动物将比距离更近的斑块中的动物在基因上更相似，但如果附近斑块具有不同的栖息地特征，这些遗传相似模式可能无法保持。这一想法是我们理解适应和进化的基础，但就快速选择的效果而言，它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。这项研究的重点是特拉华湾的东部牡蛎(Crassostrea Virgiica)，以及它们抵御水中盐分含量变化的能力。这项研究将为控制不同盐度剖面河口牡蛎生存和生长的因素提供新的见解。这三名调查人员正在与资源经理和利益相关者分享研究结果，以改善特拉华湾、切萨皮克湾和纽约的贝类恢复和牡蛎种群管理。在该项目期间，康奈尔大学的一名博士后学者和马里兰大学的研究生正在接受培训和指导。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有关牡蛎生态学的新课程材料。该项目将调查牡蛎对低盐度的耐受性是否与幼体扩散期间和定居后的生存能力选择有关。跨河口盐度带的基因流动预计将足够高，不会因为达尔文式的多代过程而导致适应性分化。相反，每一代轮回的生存能力选择预计会在小空间尺度上产生这一性状的空间变异。这种循环的世代内适应被称为表型-环境不匹配，并被假设为产生平衡的多态，但除了单基因情况外，从未进行过研究。该项目团队正在测试空间离散的选择模式，方法是首先从不同盐度地区收集牡蛎，测量它们对低盐度的耐受性的变化，然后使用全基因组测序测试这一特征与基因组变化之间的关联。实验中的低盐度挑战使世代内、基因组比较之前/之后能够识别由于强大的生存选择而发生变化的DNA变体。在相同盐度区域的幼虫、幼虫和成虫样本中，将检测候选基因和选择性中性控制基因座，以测试候选基因座变异与终生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。观察到的低盐耐受性的空间分布和与之相关的基因组变异提供了一个测试，可以明确地拒绝所有幼虫都具有相似能力的流行假设。如果幼虫的亲代来源不同，其特征对其在浮游生物中的生存能力有不同的影响，那么表型-环境不匹配可能会对种群连通性产生深远的影响。这个项目提高了人们对牡蛎种群中幼虫扩散和招募变异形成机制的理解。这个奖项反映了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。

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.