Mechanisms generating microgeographic clines in shell traits in intertidal snail populations

我的研究项目使用实验、基因组学和建模来检验这样一个假设，即直接发育的潮间带蜗牛种群内的遗传分化是由捕食者选择的空间差异和从波浪中驱逐的风险保持的。我在加拿大温哥华岛进行的长期野外捕食者入侵实验验证了一种预测，即将捕食性岸蟹移植到通常很少的海浪暴露地区，将导致周围亚圆斑蟹种群贝壳厚度的微地理斜坡进化。我模仿了非本土捕食者的入侵，为一种本土捕食性紫色岸蟹建造了混凝土避难所，允许在两个暴露在海浪中的潮间带地区捕食，那里的蜗牛(Littorina)很少有天然捕食者。在我的实验捕食梯度附近，我们的系链实验量化了捕食性岸蟹对较厚壳甲的选择，这使得我们能够对数量性状的空间模型进行参数化。在这个赠款周期中，我们将通过在一个共同的环境中培养我们实验种群的蜗牛来验证我的模型，看看是否发生了厚度的增加。然后，我们将对存在于西班牙西北部波浪暴露的岩石海岸上的两种生态型的Lsxatilis进行参数化，这两种生态型的Lsxatilis在大小、外壳厚度、隆起和着色方面显示出基于遗传的极端形态差异，并通过大小匹配交配显示部分繁殖隔离。我的博士生开发了一种新的廉价方法，使用下一代测序(NGS)和共享的计算机网络，可以在选定大小的单个蜗牛基因组样本中同时找到数千个DNA标记(单核苷酸多态(SNPs))并进行基因分型。我的本科生们已经在上岸生态型和下岸生态型之间建立了回交，并在圭尔夫大学的AquaLab中饲养着这两个完全兄弟姐妹的家庭。我的学生将寻找复杂性状(贝壳大小、形状和质量)与SNPs之间的联系。然后，我们将把与特定性状相关的SNPs映射到草莓基因组中。我们将使用这些相同的SNP标记来寻找基因组区域中有助于两个生态型之间遗传分化的异常点，并确定参与弹甲生物矿化的候选基因。一旦这个生态物种形成的模型系统得到了更好的表征，我们将在我们的实验种群中使用相同的NGS方法。我们的工作有助于预测可归因于气候变化的捕食者入侵增加的影响。我们的工作也应用于理解海洋酸化对钙化无脊椎动物之间捕食者-猎物相互作用的影响。**

My research program uses experiments, genomics, and modelling to test the hypothesis that genetic divergence within populations of direct-developing intertidal snails is maintained by spatial variation in selection by predators and by the risk of dislodgement from waves. My long-term field predator invasion experiments on Vancouver Island, Canada test the prediction that transplanting predatory shore crabs into wave-exposed areas where they are normally rare will cause evolution of a microgeographic cline in shell thickness in the surrounding populations of Littorina subrotundata. I mimicked an invasion of non-indigenous predators by building concrete refuges for a native predatory purple shore crab that allows access to prey in two wave-exposed intertidal areas where there are few natural predators on snails (Littorina). Our tethering experiments to quantify selection by predatory shore crabs for thicker shell armour in L. subrotundata near my experimental predation gradient allow us to parameterize my spatial model of a quantitative trait. During this grant cycle we will validate my model by culturing snails from our experimental populations in a common environment to see if increases in thickness have occurred. We will then parameterize my model for two ecotypes of L. saxatilis present on wave-exposed rocky shores in NW Spain that show extreme genetically-based morphological divergence for size, shell thickness, ridging and colouration and partial reproductive isolation through size-assortative mating. My Ph.D. student has developed a new inexpensive method using Next Generation Sequencing (NGS) and a shared computer network to simultaneously find and genotype thousands of DNA markers (Single Nucleotide Polymorphisms (SNPs)) in a size-selected sample of individual snail genomes. My undergraduate students have created backcrosses between the upper- and lower-shore ecotypes of L. saxatilis and are rearing the full-sibling families in the University of Guelph's AquaLab. My students will look for associations between complex traits (shell size, shape, and mass) and SNPs. We will then map the SNPs associated with a particular trait onto the draft L. saxatilis genome. We will use these same SNP markers to find outlier loci in genomic regions contributing to genetic differentiation between the two ecotypes and identify candidate genes involved in biomineralization of shell armour. Once this model system for ecological speciation is better characterized, we will use the same NGS methodology on our experimental populations of L. subrotundata. Our work contributes to predicting the effects of increased rates of predator invasions attributable to climate change. Our work also has applications to understanding the effects of ocean acidification on predator-prey interactions between calcified invertebrates. **