Differential Adaptation to Plant Toxins: The role of Chemically-mediated Selection in Reproductive Isolation between Mammalian Herbivores.

动物与环境相互作用的最基本方式之一是通过饮食。众所周知，野鼠(或袋鼠)专门研究野生有毒的食用植物。这个项目测试了一种假设，即伍德罗通过肝脏解毒酶(生化催化剂)的组合以及肠道微生物的活动来克服它们食物中的某些植物毒素。这一假说将在自然环境中进行验证，在自然环境中，两种林蛙在急剧的栖息地转变时相互接触。每个物种主要在一个或另一个栖息地发现，似乎专门研究特定于栖息地的有毒植物。该项目将审查每个物种是否对其原生栖息地的植物毒素进行了独特的适应，从而使它们无法靠邻近栖息地提供的食物维持自己的生活。因此，这些化学介导的生态适应可能会限制物种之间的遗传交换或杂交，并在维持它们的区别方面发挥重要作用。因此，这些成果将扩大对自然界中生物多样性及其管理的理解。对于食草动物来说，他们的大多数食物中发现的植物化学物质会影响生长、健康和对饮食变化的反应。因此，这项研究将对人类食用哺乳动物的生产、改良和安全具有重要意义。这项研究将为众多学生提供培训，并将允许扩大目前的高中教育项目，在该项目中，教师和他们的学生参与为期一周的动手项目，重点是人类对特定化学物质味道敏感的遗传基础。这项研究旨在确定跨越尖锐生态边界的哺乳动物杂交区的基因-表型-环境相互作用的机制。该系统需要两种木鱼(新毛目)，它们在急剧的生态过渡中杂交，但占据不同的栖息地，并维持具有不同毒素谱的栖息地特定的食物。林蛙通常专门研究剧毒的食用植物，但暴露在新型植物毒素下会产生严重的新陈代谢成本。被检验的假设是，食物专门化和栖息地/食物转换的成本是林草系统中强烈的基因型-表型-环境关系背后的主要选择力量。此外，由于在个体向植物性饮食过渡的生命早期阶段，对杂交种的强烈选择已经被证明，另一个需要检验的假设是，许多杂交种可能无法代谢亲本饮食中的任何一种。为了验证这些假说，将结合实地研究和实验室实验来量化饮食中介选择的模式(代谢组学，目标1)、机制(基因表达和肠道微生物组，目标2)和与生态相关的结果(表现，目标3)。将对不同基因类型类别(即纯种和杂交种)暴露于特定栖息地的饲料进行实验操作，以建立这些饲料的代谢过程模式，确定与接触这些饲料相关的潜在肝脏基因表达和肠道微生物群落特征，并量化与食用这些饲料相关的能量成本。与这项基于饮食的生态适应研究相关的生态学和进化论原理将被转化为加强目前的高中推广计划，这些计划侧重于人类对特定化学物质味道敏感的遗传基础。

One of the most fundamental ways that an animal interacts with its environment is through its diet. Woodrats (or packrats) are known to specialize on particularly toxic food plants in the wild. This project tests the hypothesis that woodrats overcome certain plant toxins in their diet through a combination of liver detoxification enzymes (biochemical catalysts) as well as through the activity of their gut microbes. The hypothesis will be tested in a natural setting where two species of woodrats come into contact with each other at a sharp habitat transition. Each species is primarily found in one habitat or the other, and appears to specialize on habitat-specific toxic plants. The project will examine whether each species is uniquely adapted to the plant toxins in their native habitat such that they would not be able to sustain themselves on the diet available in the adjacent habitat. As such, these chemically-mediated ecological adaptations may limit genetic exchange, or hybridization, between the species and play an important role in maintaining their distinction. These results will therefore expand understanding of biodiversity and its management in nature. For herbivores, plant chemicals found in most of their food items affect growth, health, and response to changes in diet. Thus, this research will have relevance to production, improvement, and safety of mammalian animals used as food by humans. This research will provide training for numerous students and will allow expansion of a current high school education program wherein teachers and their students participate in a week-long, hands on program focused on the genetic basis of sensitivity in humans to the taste of particular chemicals.This research aims to identify the mechanisms underlying genotype-phenotype-environment interactions across a mammalian hybrid zone that spans a sharp ecological boundary. The system entails two species of woodrat (Neotoma) that hybridize across a sharp ecological transition but occupy distinct habitats and maintain habitat-specific diets with distinct toxin profiles. Woodrats often specialize on highly toxic food plants, but exposure to novel plant toxins generates severe metabolic costs. The hypothesis tested is that diet specialization and the cost of habitat/diet switching is the primary selective force underlying the strong genotype-phenotype-environment relationship in the woodrat system. Further, because strong selection against hybrids during early stages of life, when individuals are transitioning to a plant-based diet, has been demonstrated previously, another hypothesis to be tested is that many hybrids may not be capable of metabolizing either parental diet. To test these hypotheses, field studies and laboratory experiments will be integrated to quantify the pattern (metabolomics, Aim 1), mechanisms (gene expression and gut microbiome, Aim 2), and ecologically-relevant outcome (performance, Aim 3) of diet-mediated selection. Exposure of various genotypic classes (i.e. pure and hybrid woodrats) to habitat-specific diets will be experimentally manipulated to establish patterns of metabolic processing of these diets, identify the underlying liver gene expression and gut microbial community profiles associated with exposure to these diets, and quantify the energetic costs associated with consumption of these diets. The ecological and evolutionary principles associated with this research in diet-based ecological adaptation will be translated to augment current high school outreach programs that focus on the genetic basis of sensitivity in humans to the taste of particular chemicals.