Department of Invertebrate Zoology, Smithsonian Institution, National Museum of Natural History, 10th and Constitution Ave NW, Washington DC 20560, USA.
United States Fish and Wildlife Service, Southeast Conservation Genetics Lab, Warm Springs Fish Technology Center, Auburn, AL 36849, USA; School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL 36849, USA.
Mol Phylogenet Evol. 2019 Jul;136:87-103. doi: 10.1016/j.ympev.2019.04.009. Epub 2019 Apr 8.
Juga is a genus of freshwater gastropods distributed in Pacific and Interior drainages of the Pacific Northwest from central California to northern Washington. The current classification has relied heavily on features of the shell, which vary within and across drainages, and often intergrade without sharp distinctions between species. The only previous molecular analysis included limited population sampling, which did not allow robust assessment of intra- versus interspecific levels of genetic diversity, and concluded almost every sampled population to be a distinct OTU. We assembled a multilocus mitochondrial (COI, 16S) and nuclear gene (ITS1) dataset for ∼100 populations collected across the range of the genus. We generated primary species hypotheses using ABGD with best-fit model-corrected distances and further explored our data, both individual gene partitions and concatenated datasets, using a diversity of phylogenetic and species delimitation methods (Bayesian inference, maximum likelihood estimation, StarBEAST2, bGMYC, bPTP, BP&P). Our secondary species delimitation hypotheses, based primarily on the criterion of reciprocal monophyly, and informed by a combination of geography and morphology, support the interpretation that Juga comprises a mixture of geographically widespread species and narrow range endemics. As might be expected in taxa with low vagility and poor dispersal capacities, analysis of molecular variance (AMOVA) revealed highly structured populations with up to 80% of the observed genetic variance explained by variation between populations. Analyses with bGMYC, bPTP, and BP&P appeared sensitive to this genetic structure and returned highly dissected species hypotheses that are likely oversplit. The species diversity of Juga is concluded to be lower than presently recognized, and the systematics to require extensive revision. Features of the teleoconch considered significant in species-level and subgeneric classification were found to be variable within some species, sometimes at a single site. Of a number of potentially new species identified in non-peer reviewed reports and field guides, only one was supported as a distinct OTU.
雅佳蜗牛属是分布于太平洋和太平洋西北部内陆流域的淡水腹足纲动物，从加利福尼亚州中部到华盛顿州北部。目前的分类主要依赖于壳的特征，这些特征在流域内和流域间都有变化，而且经常在物种间没有明显的区别而相互渐变。以前唯一的分子分析只包括有限的种群抽样，这不能很好地评估种内和种间遗传多样性的水平，并且几乎得出每个抽样种群都是一个独特的 OTU 的结论。我们为该属分布范围内收集的约 100 个种群组装了一个多基因线粒体（COI、16S）和核基因（ITS1）数据集。我们使用 ABGD 生成了初步的物种假设，最佳拟合模型校正距离，并进一步使用多种系统发育和物种界定方法（贝叶斯推断、最大似然估计、StarBEAST2、bGMYC、bPTP、BP&P）探索了我们的数据，包括单个基因分区和串联数据集。我们的次要物种界定假设主要基于互惠单系性标准，并结合地理和形态学信息，支持以下解释：雅佳蜗牛属由地理分布广泛的物种和狭窄分布的特有种组成。正如在迁移能力低和扩散能力差的类群中可能预期的那样，基于分子方差（AMOVA）的分析揭示了高度结构化的种群，观察到的遗传变异中有高达 80%是由种群间的变异解释的。bGMYC、bPTP 和 BP&P 的分析似乎对这种遗传结构敏感，并返回了高度分裂的物种假设，这些假设很可能过度分裂。雅佳蜗牛属的物种多样性被认为低于目前的认识水平，系统发育需要广泛修订。在种级和亚属分类中被认为重要的后肾壳特征在一些物种中是可变的，有时在一个单一的地点也是如此。在非同行评审报告和野外指南中确定的一些潜在新物种中，只有一个被支持为一个独特的 OTU。
