Collaborative Research: Plasticity, Selection, and Divergence in Stream Fishes of the Hawaiian Islands

适应性特征的差异通常与环境变化相关，但可能来自两个不同的来源：基因分化，或表型可塑性，即单一基因编码多种表型的能力。区分这些机制是进化生物学的核心挑战。夏威夷溪流鱼类提供了一个极好的系统，可以直接测量导致形态和功能变化的进化机制，以响应环境的变化。夏威夷溪流原生的五种鱼都是两栖动物：幼虫在上游孵化，但很快被冲到海洋中，在那里它们最多发育六个月，然后回到淡水中。对于三个物种来说，返回需要爬上几十米高的垂直瀑布才能到达成年栖息地。然而，最古老的(考艾岛)和最年轻的(夏威夷)岛之间的成年栖息地差别很大。夏威夷的瀑布靠近海岸，这使攀登能力得到了提升，以躲避非攀登的捕食者；相比之下，考伊安瀑布位于遥远的内陆，随着鱼类向上游迁徙，它更加注重躲避捕食者。生物力学模型预测，这些不同的需求将选择不同的体型。这个项目是生物机械学家、种群遗传学家、形态学家和水生生态学家的合作，旨在测试这样一个假设，即自然选择通过遗传分化和适应性表型可塑性的组合，促进了溪流虾虎鱼的适应性分化，以应对夏威夷和考阿岛之间不同的环境挑战。将对攀缘虎鱼和非攀缘虎鱼进行一系列互补研究。目标是：(1)评估夏威夷和考阿岛上几个溪流亚群的幼体和成体的形态差异，并测试与溪流环境差异的相关性；(2)评估攀爬和捕食对虎鱼施加的选择强度，并测试夏威夷和考艾岛种群之间的性能差异；(3)评估夏威夷和考阿岛上几个溪流中的童虫和成虫的遗传差异，并测试这些物种中基因流动的不同模式；(4)进行常见的花园捕食者暴露实验，以评估岛屿亚群基于遗传的局部适应和环境诱导的表型可塑性水平。这项工作将为研究促进生物形态和功能对环境的响应的相互作用机制提供一个模型。该项目涉及以研究为重点(克莱姆森)和以教学为中心(圣克劳德州立大学)的机构之间的合作，并将促进对本科生和研究生进行遗传学、形态学和功能生物学的综合培训，包括夏威夷水产资源部(DAR)的当地实习生。与DAR的合作将为水管理决策提供信息，以便在夏威夷限制使用人流的有害影响，帮助保护这些特有的淡水鱼。

Differences in adaptive traits often correlate with environmental variation, but can arise from two different sources: differentiation of genes, or phenotypic plasticity, the capacity of a single genotype to encode multiple phenotypes. Distinguishing between these mechanisms is a central challenge in evolutionary biology. Hawaiian stream fishes provide a superb system for directly measuring the evolutionary mechanisms leading to changes in form and function in response to environmental variation. The five fish species native to Hawaiian streams are all amphidromous: larvae hatch upstream but are quickly swept to the ocean, where they develop up to six months before returning to freshwater. For three species, returns require climbs of vertical waterfalls tens of meters tall before reaching adult habitats. However, adult habitats differ strongly between the oldest (Kaua'i) and youngest (Hawai'i) islands. Hawaiian waterfalls are close to shore, placing a premium on climbing ability to escape non-climbing predators; in contrast, Kauaian falls are far inland, placing a premium on predator evasion as fish migrate upstream. Biomechanical models predict these contrasting demands will select for divergent body shapes. This project is a collaboration among a biomechanist, a population geneticist, a morphologist, and an aquatic ecologist to test the hypothesis that natural selection has promoted adaptive divergence in stream gobies in response to differing environmental challenges between Hawai'i and Kaua'i through a combination of genetic differentiation and adaptive phenotypic plasticity. A series of complementary studies on the climbing goby Sicyopterus stimpsoni and the non-climbing goby Stenogobius hawaiiensis will be conducted. Goals are to: (1) evaluate morphological divergence in juveniles and adults from several stream subpopulations on Hawai'i and Kaua'i, and test for correlations with environmental differences in streams; (2) evaluate the strength of selection imposed on gobies by climbing and predation, and test for performance differences between populations from Hawai'i and Kaua'i; (3) evaluate neutral genetic divergence in juvenile and adult S. stimpsoni and S. hawaiiensis from several streams on Hawai'i and Kaua'i, and test for differential patterns of gene flow in these species; (4) conduct common garden predator exposure experiments to evaluate levels of genetically based local adaptation and environmentally induced phenotypic plasticity among island subpopulations. This work will provide a model for research on the interactive mechanisms promoting the evolution of organismal form and function in response to environment. This project involves collaboration of research-focused (Clemson) and teaching-centered (St. Cloud State) institutions, and will promote integrative training in genetics, morphology, and functional biology for both undergraduate and graduate students, including local interns with the Hawai'i Division of Aquatic Resources (DAR). Cooperation with the DAR will inform water management decisions so that detrimental impacts of human stream use can be limited in Hawai'i, helping to protect these endemic freshwater fishes.