EAGER: Evaluating a drought-driven hypothesis for the origin of obligate apomixis

专性无融合生殖--通过种子、孢子或卵子进行无性繁殖--在整个生命树上反复进化，在从动物(如爬行动物、昆虫和鱼类)到被子植物(开花植物)和其他维管束植物的各种生物中都有。尽管它的起源很多，而且它们之间在生态和进化上有有趣的相似之处，但人们对这种可遗传生殖综合征的原因和长期后果知之甚少。最近的一些研究表明，干旱或周期性的水分限制可能是驱动专性无融合生殖反复进化的关键。该项目结合环境、发展和进化数据来评估干旱假说，利用蕨类植物作为模型系统。蕨类植物是这项工作的理想对象，因为与其他生物相比，观察减数分裂(即产生孢子/配子的特殊细胞分裂)更容易、更有效。此外，这项研究弥合了下一代研究人员在各种前沿和经典方法的技术专长方面的代沟；它刺激了跨学科的本科生、研究生和博士后研究，强调了博物馆标本在解决基本生物学问题方面的价值和相关性；它扩大了墨西哥和拉丁美洲的国际科学合作。此外，由于专性无融合生殖在农业中的应用(作为稳定最佳基因类型的工具)非常令人垂涎，但又不愿使用，这项研究有可能产生对人类具有实际意义的有价值的见解，特别是在医药和全球粮食生产方面。这项研究结合了遗传、空间、环境和生活史数据，涉及多个进化和生态尺度上的大约47个物种，其中包括Myriopteris Fée，这是蕨亚科Cheilanthoideae中一个得到很好支持的支系。初步数据与新收集的生殖特征(核型、配子体发育和孢子大小/数量)、气候和微生境的观察相结合，并建立了完全采样的、经过时间校准的系统发育图，以严格询问干旱与专性无融合生殖进化之间的关系。具体地说，这些结果被用来解决三个主要问题：系统发育惯性是否决定了专性无融合生殖或相关特征在局部分支中的分布？微生态位能预测北美沙漠，包括奇瓦瓦沙漠、索诺兰沙漠和莫哈韦沙漠中的专性无融合生殖吗？而且，微生境是否与专性无融合生殖或其在整个局域分支的组成特征显著相关？重要的是，这项工作还有助于解决多翅目昆虫内部不同的、以前未描述的、杂交和多倍体谱系之间的复杂进化关系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Obligate apomixis—asexual reproduction by seed, spore, or egg—has evolved repeatedly across the tree of life, in diverse organisms ranging from animals (such as reptiles, insects, and fishes) to angiosperms (flowering plants) and other vascular plants. Despite its many origins, and intriguing ecological and evolutionary parallels among them, little is known regarding the causes and long-term consequences of this heritable reproductive syndrome. Some recent studies have proposed that drought, or periodic water limitation, could be key to driving the repeated evolution of obligate apomixis. This project unites environmental, developmental, and evolutionary data to evaluate the drought hypothesis, leveraging ferns as a model system. Ferns are ideal for this work because observing meiosis (i.e., the specialized cell division that produces spores/gametes) is easy and efficient compared to other organisms. Additionally, this study bridges generational gaps in technical expertise among next-generation researchers for a variety of cutting-edge and classical approaches; it stimulates interdisciplinary undergraduate, graduate, and postdoctoral research, emphasizing the value and relevance of museum specimens for addressing fundamental biological questions; and it expands international scientific collaborations in Mexico and Latin America. Furthermore, because obligate apomixis is highly coveted for, yet recalcitrant to, use in agricultural applications (as a tool for stabilizing optimal genotypes), this study has the potential to yield valuable insights with practical implications for humanity, especially regarding medicine and global food production. This research combines genetic, spatial, environmental, and life history data, across multiple evolutionary and ecological scales, for around 47 species comprising Myriopteris Fée, a well-supported clade in the fern subfamily Cheilanthoideae (Pteridaceae). Preliminary data are integrated with newly-gathered observations of reproductive traits (karyotype, gametophyte development, and spore size/number), climate and microhabitat, and a fully-sampled, time-calibrated phylogeny to rigorously interrogate the relationship between drought and the evolution of obligate apomixis. Specifically, these results are leveraged to address three main questions: Does phylogenetic inertia shape the distribution of obligate apomixis, or associated traits, within the focal clade? Does macroecological niche predict obligate apomixis among deserts of North America, including the Chihuahuan, Sonoran, and Mojave? And, is microhabitat significantly associated with obligate apomixis or its constituent traits across the focal clade? Importantly, this work also serves to resolve complex evolutionary relationships among diverse, previously undescribed, hybrid and polyploid lineages within Myriopteris.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.