Digestive Specializations for Herbivory in Marine Fishes: Genetic Adaptation and Phenotypic Plasticity in Gut Structure and Function in Pricklebacks

海洋鱼类在肠道结构和功能方面对草食的需求仍然知之甚少。这项研究的动力可以概括为一个问题：什么是食草动物？为了回答这个问题，将进行饲养实验和相应的不同生物组织水平的组织学和酶分析。这项工作包括两个部分的调查，解决遗传适应和消化系统的表型可塑性在四个相关物种的海洋鱼类。在该项目的第一部分，目标是测试是否存在肠道结构和功能的遗传程序性变化，这些变化发生在个体发生的饮食从食肉动物到食草动物的转变之前。为了实现这一目标，将在一段时间内确定目标鱼的一系列消化和吸收酶的活性、位置、浓度和基因表达，在这段时间内，其中两种鱼类自然地从食肉性转变为食草性，而另外两种自然地保持食肉性。在该项目的第二部分，目的是评估肉食性和草食性鱼类肠道结构和功能的表型可塑性程度。为了实现这一目标，将在同时饲喂植物和动物的实验中确定四种目标物种的肠道结构和消化酶的调整以及身体成分的变化。本研究选择的鱼类是一个较大的进化分支中相邻分支的成员，该进化分支已被提出用于这些物种所属的科（刺背科，刺背科）。这些相关的分类群被视为这类研究的模式物种，因为这四种物种都是从食肉动物开始的，但其中两种在幼年时转为食草动物，而另外两种则终生保持食肉动物。两部分研究中获得的组织学和酶学数据将通过比较生物学方法作为表型特征映射到棘鱼系统发育树上，以了解是否可以推断该鱼类家族的食草性适应和饮食变化的进化轨迹。该研究有可能为了解海洋鱼类的肠道结构和功能做出重大贡献，并提供一种可应用于其他海洋系统的模型方法。在个体发育和系统发育的背景下，使用一系列强大的原位组织化学和分子技术，将促进对海洋鱼类消化过程的了解，并拓宽海洋脊椎动物食草动物的视角。该项目还将通过让不同学术水平、不同性别和种族背景的人参与进来，帮助推进科学教育和开发人力资源。教学、培训和学习将通过参与的多样性和获得新的实验室设备而得到加强。

Horn 9906857The requirements for herbivory in terms of gut structure and function remain poorly understood for marine fishes. The impetus for this research can be framed as a question: What does it take to be a herbivore? To answer this question, feeding experiments and accompanying histological and enzymatic analyses at different levels of biological organization will be performed. The work involves a two-part investigation addressing genetic adaptation and phenotypic plasticity of the digestive system in four related species of marine fishes. In the first part of the project, the objective is to test whether there are genetically programmed changes in gut structure and function that precede an ontogenetic dietary shift from carnivory to herbivory. To meet this objective, the activity, location, concentration and gene expression of a broad array of digestive and absorptive enzymes will be determined in the target fishes that have been fed a consistent animal diet during an interval in which two of the species naturally switch from carnivory to herbivory and the other two naturally remain carnivorous. In the second part of the project, the objective is to assess the degree of phenotypic plasticity in gut structure and function shown by carnivorous and herbivorous fishes. To meet this objective, gut structure and digestive enzyme adjustments and body composition changes will be determined during experiments in which the four target species are fed both a plant and an animal diet. The fishes chosen for this study are members of adjacent clades in a larger clade of a phylogeny that has been proposed for the family (Stichaeidae, pricklebacks) to which these species belong. These related taxa are viewed as model species for this type of research because all four begin life as carnivores, but two switch to herbivory as small juveniles while the other two remain carnivorous throughout life. The histological and enzymatic data obtained in the two-part study will be mapped as phenotypic traits onto the stichaeid phylogenetic tree using comparative biology methods to see whether adaptations for herbivory and the evolutionary trajectory of diet change can be inferred for this family of fishes. The research has the potential to make a substantial contribution to the understanding of gut structure and function in marine fishes and offers a model approach that can be applied to other marine systems. The use of an array of powerful in situ histochemical and molecular techniques in the context of both ontogeny and phylogeny should advance the knowledge of digestive processes among marine fishes in general and broaden the perspective on marine vertebrate herbivores. The project will also help advance science education and develop human resources by involving persons from a full range of academic levels and from different gender and ethnic backgrounds. Teaching, training and learning will be enhanced by this diversity of involvement and by the acquisition of new laboratory equipment.