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

这个项目的重点是两栖动物的嗅觉系统是如何在水中和空气中发挥作用的。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，这一历史转变反映了当前的发育转变，因为它们从水生幼虫转变为陆生幼崽。像其他感觉系统一样，嗅觉系统必须能够在这一发展转变的两种环境中进行调整和发挥作用。该项目通过研究八种相关蝾螈物种的嗅觉形态和基因表达模式开辟了新的领域，这些物种具有广泛的生活史，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。该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的嗅觉组织模式是否一致？(2)直接发育的陆生物种是否丧失了水感嗅觉成分？(3)在幼虫期重新进化的物种是否会重新获得水感嗅觉成分？这项工作将在洪堡州立大学进行，这是一所位于加州北部沿海农村的西班牙裔服务机构。它将直接支持15-20名本科生和2名研究生进行实践研究，提高他们的技能，从而促进他们的职业和就业前景。这项研究将融入课堂，每年约有300名学生受益。公共宣传部分将包括向当地社区成员进行讲座，提高对进化和发展的科学素养，并促进对这一未被充分研究的脊椎动物群体的欣赏。本项目将研究不同发育模式的进化如何影响大多数种类的蝾螈（多齿螈或无肺蝾螈）嗅觉系统的结构和功能。本文将研究八种多齿兽和一种多齿兽外群的嗅觉形态和基因表达模式。使用的技术将包括传统组织学来比较嗅觉器官的基本结构，透射电镜和扫描电镜来建立嗅觉受体神经元和支持细胞的形态分类，微ct扫描和三维重建来提供嗅觉器官整体解剖结构的视觉图像，神经元追踪来建立嗅觉受体神经元连接到大脑的途径，以及嗅觉标记基因的蛋白质和mRNA定位。这项工作将首次阐明在明确的系统发育框架内，在水和空气中，幼虫和成虫的嗅觉进化模式。通过这样做，它将使人们更好地理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的进化出现相关的变化。共有15-20名本科生和2名研究生将直接参与该项目，研究将被纳入5门课程，约300名学生参加。这项研究还将在该机构的自然历史博物馆和当地一家咖啡馆的科学系列讲座中向公众展示。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。

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.