RUI: Smelling in water and air: Evolution of olfaction in plethodontid salamanders

这个项目的重点是如何改变两栖动物的嗅觉系统，使其在水和空气中发挥作用。脊椎动物从水到陆地的出现是脊椎动物进化的主要转变之一。对于许多现存的两栖动物来说，这一历史转变反映在目前的发育转变中，因为它们从水生幼虫蜕变为陆地幼虫。与其他感官系统一样，嗅觉系统必须能够在这两种环境中进行调节，并在发育过程中发挥作用。这个项目通过研究8个相关物种的嗅觉形态和基因表达模式取得了新的进展，这些物种的生活史范围很广，从典型的变态幼虫到没有自由生活的幼虫阶段的直接发育，再到二次再进化的幼虫。这项研究将回答以下问题：(1)无论进化历史如何，具有相同发育模式的物种之间的嗅觉组织模式是否一致？(2)陆生、直接发育的物种是否失去了水感嗅觉成分？(3)经过幼虫期再进化的物种是否重新获得了水感嗅觉成分？这项工作将在洪堡州立大学进行，这是一所位于加利福尼亚州北部海岸农村的拉美裔服务机构。它将直接支持15-20名本科生和两名研究生的实践研究，提高他们的技能，从而促进他们的职业生涯和就业前景。这项研究将被整合到课堂上，每年将使大约300名学生受益。公共推广部分将包括对当地社区成员的讲座，提高对进化和发展的科学素养，并促进对这一未被研究的脊椎动物群体的欣赏。本项目将研究替代发展模式的演变如何影响最特殊的火蜥蜴家族--多齿火蜥蜴或无肺火蜥蜴的嗅觉系统结构和功能。我们将研究8种多齿目动物和1种外类群物种的嗅觉形态和基因表达模式，它们跨越了广泛的发育模式。将使用的技术包括比较嗅觉器官基本结构的传统组织学，建立嗅觉感受器神经元和支持细胞的形态分类的透射和扫描电子显微镜，提供整体嗅觉器官解剖的可视图像的MicroCT扫描和3-D重建，建立嗅觉感受器神经元连接到大脑的通路的神经元示踪，以及嗅觉标记基因的蛋白质和mRNA定位。这项工作将首次在一个明确的系统发育框架内阐明在水和空气中、在幼虫和成虫中嗅觉的进化模式。通过这样做，它将使人们更好地了解现存两栖动物的嗅觉系统是如何进化的，以及与陆地上四足动物进化出现相关的变化。共有15-20名本科生和两名研究生将直接参与该项目，研究将被纳入五门课程，招收约300名学生。这项研究还将在该机构的自然历史博物馆和当地咖啡馆的一系列科学讲座上向公众展示。这一奖项反映了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。

This project focuses on how the olfactory system of amphibians is modified to function in water and in air. The emergence of vertebrate animals from water onto land was one of the major transitions of vertebrate evolution. For many living amphibians, this historical transition is mirrored by a current developmental transition, as they metamorphose from an aquatic larva to a terrestrial juvenile. Like other sensory systems, the olfactory system must be able to adjust and function in both environments across this developmental transition. This project breaks new ground by examining olfactory morphology and gene expression patterns across eight related salamander species with a wide range of life histories, ranging from typical larvae with metamorphosis, to direct development with no free-living larval stage, to secondarily re-evolved larvae. The study will answer the following questions: (1) Are patterns of olfactory organization consistent across species with the same developmental mode, regardless of evolutionary history? (2) Are water-sensing olfactory components lost in terrestrial, direct-developing species? (3) Do species that have re-evolved a larval period regain water-sensing olfactory components? This work will take place at Humboldt State University, an Hispanic Serving Institution located on the rural northern coast of California. It will directly support 15-20 undergraduate and two graduate students in hands-on research, enhancing their skills and thereby furthering their careers and job prospects. The research will be integrated into classes, benefitting approximately 300 students per year. A public outreach component will involve lectures to local community members, increasing scientific literacy on evolution and development and promoting appreciation for this understudied group of vertebrates.This project will examine how the evolution of alternative developmental modes impacts olfactory system structure and function in the most speciose family of salamanders, the plethodontid or lungless salamanders. Olfactory morphology and gene expression patterns of eight plethodontid species and one outgroup species that span a wide range of developmental modes will be examined. Techniques used will include traditional histology to compare the basic structure of the olfactory organs, transmission and scanning electron microscopy to establish morphological classes of olfactory receptor neurons and supporting cells, microCT scanning and 3-D reconstruction to provide a visual image of overall olfactory organ anatomy, neuronal tracing to establish pathways of olfactory receptor neuron connection to the brain, and protein and mRNA localization of olfactory marker genes. This work will for the first time elucidate patterns of olfactory evolution with respect to olfaction in water and air, in larvae and adults, within an explicit phylogenetic framework. By doing so, it will allow a better understanding of how the olfactory system evolves in living amphibians, and of changes associated with the evolutionary emergence of tetrapods onto land. A total of 15-20 undergraduates and two graduate students will participate directly in the project, and the research will be incorporated into five courses that enroll approximately 300 students. The research will also be presented to the public at the institution’s natural history museum and at a science lecture series at a local coffeehouse.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.