Dimensions: Convergent Evolution of Nectarivory and its Association with High-Altitude Adaptation in Hummingbirds and Sunbirds

研究产生生物多样性的机制的一个有力方法是关注趋同进化的实例。趋同进化发生在同一性状独立进化两次或更多次时，提供了适应性进化的自然复制。例如，在北美和南美的蜂鸟，以及非洲、亚洲和澳大拉西亚的太阳鸟、捕蜘蛛者和啄花鸟中，以花蜜为食及其伴随的形态适应（例如，长而尖的喙和特殊的舌头结构）已经独立地进化出来。本项目将对这两类鸟类进行研究，以更好地了解导致相关基因和生理趋同进化的生态和遗传因素。这项研究将调查品尝糖、代谢酒精以及在氧气较少的高海拔地区生活的能力的趋同进化。它还将研究生活在鸟类内脏中的微生物群落的趋同。这项研究将揭示相同的遗传变化对功能相似的生理性状的进化负责的频率，并将导致对适应和物种多样化的更好理解。该研究将形成蜂鸟、太阳鸟、猎蜘蛛鸟和啄花鸟的综合进化树，为保护这些占鸟类物种多样性约5%的鸟类提供重要资源。本项目将培养3名研究生和1名博士后，在生物信息学、功能生理学、行为生态学、遗传学和系统遗传学的研究技术方面进行整合。它还将在复杂的分子遗传技术和生理学研究方面培养多达10名本科生，这将为他们提供宝贵的研究经验。这笔拨款将通过与运营“理解进化”网站的教育工作者合作，促进公众对科学的理解，该网站将帮助为教师开发课程材料，在蜂鸟和太阳鸟多样化的背景下解释适应和趋同进化等进化概念。该项目将研究提高低氧抗性性状的趋同，与蜜汁有关性状的趋同，并将研究与蜜汁有关的性状如何在高海拔环境中趋同，这是蜂鸟和太阳鸟多样化的特征。在遗传层面，研究小组将研究与蜜汁有关的基因（即糖味受体、酒精代谢基因）和赋予耐缺氧能力的基因途径（即血红蛋白、OXPHOS、缺氧诱导因子途径）。此外，研究人员将对食蜜鸟肠道样本中的16S核糖体RNA基因进行测序，以研究微生物群落。在功能层面上，研究小组将测试基因变化如何改变表型，这对生物体功能和随后进入新生态位的多样化都很重要。为了实现这一目标，研究小组将进行生理测试来测量耐缺氧能力，量化羽毛样本中的饮食酒精暴露（以发酵花蜜的形式），从肠道微生物的16S rRNA序列中预测代谢功能，在实验室中分析基因变异之间的功能差异（例如，测量不同味觉受体变异的反应性的细胞培养分析），并进行味觉辨别能力的行为测试。在系统发育水平上，研究小组将研究基因和表型的进化史，以揭示两种鸟类辐射内部和之间的趋同进化实例。最后，该团队将整合所有遗传、功能和系统发育数据，以评估：(1)趋同遗传进化的普遍性如何随时间变化；(2)高海拔环境下，性状套件如何共同进化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A powerful way to study mechanisms that generate biodiversity is to focus on instances of convergent evolution. Convergent evolution occurs when the same trait evolves independently two or more times, providing natural replicates of adaptive evolution. For example, feeding on nectar and its accompanying morphological adaptations (e.g., long tapered bills with specialized tongue structures) have evolved independently in hummingbirds in North and South America, and in the sunbirds, spiderhunters, and flowerpeckers of Africa, Asia, and Australasia. This project will study these two groups of birds to better understand the ecological and genetic factors that lead to convergent evolution in associated genes and physiology. The research will investigate convergent evolution in the ability to taste sugar, metabolize alcohol, and live at high altitudes where there is less oxygen. It will also study convergence in the microbial communities living in the guts of the birds. This study will reveal how often the same genetic changes are responsible for the evolution of functionally similar physiological traits, and will lead to an improved understanding of adaptation and species diversification. The research will result in comprehensive evolutionary trees for hummingbirds, sunbirds, spiderhunters, and flowerpeckers, which will be an important resource for the conservation of these diverse avian groups that together constitute ~5% of bird species diversity. This project will train three graduate students and a postdoctoral fellow in research techniques integrating bioinformatics, functional physiology, behavioral ecology, genetics, and phylogenetics. It will also train up to ten undergraduates in sophisticated molecular genetic techniques and physiological research, which will give them valuable research experience. This grant will promote public understanding of science through a collaboration with educators who run the "Understanding Evolution" website, who will help to develop course materials for teachers that explain evolutionary concepts like adaptation and convergent evolution in the context of the diversification of hummingbirds and sunbirds.This project will study convergence in traits that improve hypoxia resistance, convergence in traits related to nectarivory, and will investigate how traits related to nectarivory may converge in high-altitude environments that characterize the diversification of hummingbirds and sunbirds. On the genetic level, the research team will study genes related to nectarivory (i.e., sugar taste receptors, alcohol metabolism genes) and gene pathways that can confer hypoxia resistance (i.e., hemoglobin, OXPHOS, and hypoxia-inducible factor pathways). In addition, the researchers will sequence 16S ribosomal RNA genes from gut samples of nectarivorous birds to study microbial communities. On the functional level, the research team will test how genetic changes have altered phenotypes important for both organismal function and subsequent diversification into new ecological niches. To accomplish this, the team will perform physiological tests to measure hypoxia resistance, quantify dietary alcohol exposure (in the form of fermented nectar) from feather samples, predict metabolic functions of gut microbes from their 16S rRNA sequences, assay functional differences among genetic variants in the lab (e.g., cell-culture assays that measure responsiveness of different taste receptor variants), and conduct behavioral tests of taste discrimination abilities. On the phylogenetic level, the research team will study the evolutionary history of genes and phenotypes to reveal instances of convergent evolution within and between the two avian radiations. Finally, the team will integrate all genetic, functional, and phylogenetic data to evaluate: (1) how the prevalence of convergent genetic evolution changes with time, and (2) how suites of traits co-evolve in response to high-altitude environments.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.