DISSERTATION RESEARCH: The conflicting effects of gene flow in a geographic mosaic of predator-prey coevolution

这项研究将测试普通吊袜带蛇和它们的有毒猎物太平洋鳗之间的共同进化军备竞赛中基因流的冲突效应。生态群落的结构和复杂性是由相互作用的物种的共同进化形成的。负面相互作用，如捕食者-猎物关系，通常以持续和快速适应为特征；每个物种都必须不断适应和反适应其天敌共同进化的防御。理论预测，迁徙和种群间遗传物质的交换(称为基因流的过程)将对局部适应对抗性相互作用产生两个重要但相互冲突的影响。基因流动通常被认为会使种群间的遗传变异同质化，并阻碍当地的适应。相反，基因流动和迁移可能在将有益的突变传播到新的种群和促进快速适应变化方面发挥关键作用。这项研究将为理解持续的、往往是快速的进化变化背后的遗传动力奠定基础，这些进化变化导致跨越捕食者-猎物、宿主-寄生虫和植物-动物系统的复杂特征的巨大多样性。此外，这项研究还将有助于研究生和本科生的培训。在北美西部，吊袜蛇(Thamnophim Sirtalis)已经对河豚毒素(TTX)产生了抵抗力，河豚毒素是一种在蝾螈中发现的致命神经毒素。高抵抗力的蛇种群倾向于与剧毒的蝾螈(塔里查物种)共存，因为共同进化显然推动了捕食者和猎物武器的升级。吊袜带蛇对毒素的抵抗力在很大程度上是由于NaV1.4钠通道蛋白中关键氨基酸的替换。该项目将使用下一代DNA测序来测试蛇的基因流是否通过NaV1.4钠通道中TTX耐药突变的传播来促进对有毒蝾螈的适应。研究人员将从北美西部的束带蛇种群中产生两个独立的遗传数据集：(1)NaV1.4基因座的遗传变异，(2)与NaV1.4无关的背景遗传变异，来自双酶切限制相关DNA测序(DdRADseq)的中性单核苷酸多态性(SNPs)。然后，将分别估计每个数据集的种群结构和基因流动。两个数据集之间不一致的基因流模式将表明，相对于SNPs的中性预期，选择在哪里改变了NaV1.4单倍型的传播。例如，在基因流动和选择有利于TTX耐药突变传播的人群中，NaV1.4基因座的基因流动应该超过中性SNPs的背景变异。

This research will test the conflicting effects of gene flow in the co-evolutionary arms race between common garter snakes and their toxic prey, Pacific newts. The structure and complexity of ecological communities is shaped by the joint evolution of interacting species. Negative interactions, like predator-prey relationships, are often characterized by sustained and rapid adaptation; each species must constantly adapt and counter-adapt to the co-evolving defenses of its natural enemy. Theory predicts that migration and the exchange of genetic material among populations (a process called gene flow) will have two important, yet conflicting, effects on local adaptation to antagonistic interactions. Gene flow is generally thought to homogenize genetic variation among populations and hinder local adaptation. Conversely, gene flow and migration may play a critical role to spread beneficial mutations to new populations and promote rapid adaptive change. This research will form a foundation for understanding the genetic impetus behind sustained, and often rapid, evolutionary changes that are responsible for the tremendous diversity of complex traits that span predator-prey, host-parasite, and plant-animal systems. In addition, this study will contribute to the training of graduate and undergraduate students.In western North America, garter snakes (Thamnophis sirtalis) have evolved resistance to tetrodotoxin (TTX), an otherwise lethal neurotoxin found in the newts. Highly resistant snake populations tend to co-occur with highly toxic newts (Taricha species), as coevolution has apparently driven the escalation of armaments in both predator and prey. Toxin resistance in the garter snake is largely due to key amino acid replacements in the NaV1.4 sodium channel protein. This project will use next-generation DNA sequencing to test whether snake gene flow promotes adaptation to toxic newts through the spread of TTX-resistance mutations in the NaV1.4 sodium channel. The researchers will generate two separate genetic datasets from garter snake populations across western North America: (1) genetic variation at the NaV1.4 locus, and (2) background genetic variation, unlinked to NaV1.4, in neutral Single Nucleotide Polymorphisms (SNPs) from double digest Restriction Associated DNA sequencing (ddRADseq). Population structure and gene flow will then be estimated separately for each dataset. Discordant patterns of gene flow between the two datasets will indicate where selection has altered the spread of NaV1.4 haplotypes in relation to neutral expectations of the SNPs. For example, in populations where gene flow and selection favor the spread of TTX-resistance mutations, gene flow at the NaV1.4 locus should exceed that of background variation in the neutral SNPs.