Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY, USA.
Department of Botany, University of Wyoming, Laramie, WY, USA.
Mol Ecol. 2019 Aug;28(16):3738-3755. doi: 10.1111/mec.15175. Epub 2019 Aug 11.
Hybridization can profoundly affect the genomic composition and phenotypes of closely related species, and provides an opportunity to identify mechanisms that maintain reproductive isolation between species. Recent evidence suggests that hybridization outcomes within a species pair can vary across locations. However, we still do not know how variable outcomes of hybridization are across geographic replicates, and what mechanisms drive that variation. In this study, we described hybridization outcomes across 27 locations in the North Fork Shoshone River basin (Wyoming, USA) where native Yellowstone cutthroat trout and introduced rainbow trout co-occur. We used genomic data and hierarchical Bayesian models to precisely identify ancestry of hybrid individuals. Hybridization outcomes varied across locations. In some locations, only rainbow trout and advanced backcrossed hybrids towards rainbow trout were present, while trout in other locations had a broader range of ancestry, including both parental species and first-generation hybrids. Later-generation intermediate hybrids were rare relative to backcrossed hybrids and rainbow trout individuals. Using an individual-based simulation, we found that outcomes of hybridization in the North Fork Shoshone River basin deviate substantially from what we would expect under null expectations of random mating and no selection against hybrids. Since this deviation implies that some mechanisms of reproductive isolation function to maintain parental taxa and a diversity of hybrid types, we then modelled hybridization outcomes as a function of environmental variables and stocking history that are likely to affect prezygotic barriers to hybridization. Variables associated with history of fish stocking were the strongest predictors of hybridization outcomes, followed by environmental variables that might affect overlap in spawning time and location.
杂交可以深刻影响亲缘关系密切的物种的基因组组成和表型，并为识别维持物种间生殖隔离的机制提供了机会。最近的证据表明，物种对内的杂交结果在不同地点可能有所不同。然而，我们仍然不知道杂交结果在地理复制中变化有多大，以及是什么机制导致了这种变化。在这项研究中，我们描述了在美国怀俄明州北叉肖肖尼河流域（North Fork Shoshone River basin）的 27 个地点的杂交结果，那里有本地的黄石河鳟鱼（Yellowstone cutthroat trout）和引入的虹鳟鱼（rainbow trout）共存。我们使用基因组数据和分层贝叶斯模型来准确识别杂交个体的祖先。杂交结果在不同地点有所不同。在一些地点，只有虹鳟鱼和向虹鳟鱼方向的高级回交杂种存在，而在其他地点的鳟鱼具有更广泛的祖先，包括双亲物种和第一代杂种。相对于回交杂种和虹鳟鱼个体，后几代中间杂种较为罕见。通过基于个体的模拟，我们发现北叉肖肖尼河流域的杂交结果与我们预期的随机交配和无杂交选择的情况下的零假设有很大的偏差。由于这种偏差意味着一些生殖隔离机制起作用，以维持亲代类群和多种杂种类型，因此我们将杂交结果建模为可能影响杂交前合子障碍的环境变量和放流历史的函数。与鱼类放流历史相关的变量是杂交结果的最强预测因子，其次是可能影响产卵时间和地点重叠的环境变量。
