Collaborative Research: Does genetic load drive mating system evolution? Tests in an explicit historical context

本研究将量化历史事件与当前自然选择在形成植物交配系统中的相互作用。进化是一个持续的过程，但很大程度上依赖于过去。虽然几乎每个人都承认这一事实，但很难量化历史和当前选择压力在解释自然模式方面的相对重要性。本研究将着眼于决定美洲风铃花（Campanulastrum americanum）自花授粉与异交数量的因素。该项目将使本科生和研究生沉浸在下一代DNA序列数据的收集中，以重建研究物种的历史事件和当前选择环境的研究。将这些不同来源的数据分析成一个单一的、统一的框架，将提供对自然界中形成复杂模式的过程的更清晰的理解，并产生一个可应用于任何生物系统的预测框架。这种预测方法的广泛传播是有价值的，因为它将有助于预测物种对现代日益变化的环境的反应。植物交配系统在进化上是不稳定的，从高度异交到高度近交。这种广泛的差异为理解进化变化的最终驱动因素提供了一个极好的系统。在不同的生物等级中，不同的交配系统策略通常被解释为对当前选择环境的适应。然而，这种变异的很大一部分可能反映了在范围扩张期间对殖民化的反应的历史进化。这一观点将用北美的一种草本植物Campanulastrum americanum进行验证。在Campanulastrum americanum中，初步数据表明，在系统地理数据显示最近殖民的地方，近亲繁殖的抑制现象减少，自交配现象增多。利用距离冰川避难所一定距离的种群，研究人员将收集数据，包括RAD-seq多态性的聚合分析、固定和分离遗传负荷的温室研究、花粉限制和生殖保证的实地研究以及自花率的种群遗传推断。对这些数据的分析将确定最初与范围扩展相关的非适应性过程是否为交配系统的后期进化提供了一个允许的环境。因此，该研究框架为辨别过去和现在时间尺度上生物体变化的最终驱动因素提供了一种机制。

This research will quantify the interplay between historical events and current natural selection in shaping plant mating system. Evolution is an ongoing process but depends strongly on the past. While nearly everyone acknowledges this fact, it has been difficult to quantify the relative importance of historical and current selection pressures as explanations of patterns in nature. This research will look at the factors that have determined the amount of self-pollination versus outcrossing in the American bellflower (Campanulastrum americanum). The project will immerse undergraduate and graduate students in the collection of next-generation DNA sequence data to reconstruct historical events and studies of current selective environment in the study species. Analyses of data from these disparate sources into a single, unified framework will provide a clearer understanding of the processes shaping complex patterns in nature, and yields a predictive framework that can be applied in any biological system. Broad dissemination of this predictive approach is valuable because it will help predict the response of species to increasingly altered environments in the modern age.Plant mating systems are evolutionarily labile, ranging from highly outcrossing to highly inbreeding. This wide variation provides an excellent system for understanding the ultimate drivers of evolutionary change. Variable mating system strategies across levels of the biological hierarchy are commonly explained as adaptations to the current selective environment. A significant fraction of this variation, however, may reflect historical evolution in response to colonization during range expansion. This idea will be tested using Campanulastrum americanum, a North American herb in which preliminary data indicate reduced inbreeding depression and greater autogamy in sites where phylogeographic data suggest recent colonization. Using populations a range of distances from glacial refugia, the researchers will gather data with coalescent analysis of RAD-seq polymorphism, greenhouse studies of fixed and segregating genetic load, field studies of pollen limitation and reproductive assurance, and population-genetic inferences of selfing rates. Analyses of these data will determine whether initially non-adaptive processes associated with range expansion provided a permissive environment for later evolution of the mating system. The research framework therefore provides a mechanism for discerning the ultimate drivers of organismal change across past and present time scales.