Department of Biological Sciences, 202 Life Sciences Building, Louisiana State University, Baton Rouge, Louisiana 70808, USA.
Evolution. 2010 Jul;64(7):2070-85. doi: 10.1111/j.1558-5646.2010.00957.x. Epub 2010 Jan 21.
Fish have radiated to exploit diverse habitats, but little is known about the evolutionary lability and directionality of associated physiological specialization. Killifish of the genus Fundulus present a compelling system to explore the evolution of osmotic tolerance because closely related species have evolved to occupy most osmotic niches, and physiological osmotic tolerance data are available for most species. This study seeks to determine the number of times, and the rate at which, alternate osmotic tolerance physiologies have evolved, and to determine the directionality of physiological transitions, by mapping comparative physiology data to a molecular phylogeny for the genus. Character mapping and phylogeographic inference indicate that freshwater tolerance is derived, can evolve rapidly, has evolved several times within the genus, and that variation in osmotic tolerance contributes to defining species distributions. The derivation of alternate physiologies within Fundulus appears associated with contraction of physiological plasticity rather than shifts in tolerance ranges, and the degree of contraction is surprisingly similar across convergent physiological types. The rate of physiological transition is relatively high within Fundulus compared to other taxa, but directionality from high salt tolerance to intolerance appears to be the rule. Together, these comparative physiology and phylogenetic data yield insight into the patterns of evolution of ecological specialization.
鱼类已经辐射进化以适应各种不同的栖息地，但对于相关生理特化的进化灵活性和方向性却知之甚少。花鳉科的溪红点鲑属（Fundulus）是一个探索渗透耐受性进化的引人入胜的系统，因为密切相关的物种已经进化到可以占据大多数渗透小生境，并且大多数物种的生理渗透耐受性数据都可用。本研究旨在通过将比较生理学数据映射到该属的分子系统发育树上，确定替代渗透耐受性生理机能进化的次数和速率，并确定生理转变的方向性。特征映射和系统地理学推断表明，淡水耐受性是衍生的，可以快速进化，在属内已经进化了多次，渗透耐受性的变化有助于定义物种分布。溪红点鲑属内的替代生理机能的出现似乎与生理可塑性的收缩有关，而不是耐受范围的变化，并且在趋同的生理类型中，收缩的程度惊人地相似。与其他分类群相比，溪红点鲑属内的生理转变速度相对较高，但从高盐耐受性到不耐受性的转变似乎是普遍现象。总之，这些比较生理学和系统发育学数据为生态特化的进化模式提供了深入的见解。
