The molecular basis of phenotypic plasticity and genetic assimilation in rapidly evolving lineages of East African cichlid fishes

生物体调节其表型以响应环境刺激的能力被称为表型可塑性。传统上，它经常被视为阻碍和限制进化。然而，这一观点是有争议的，另外，West-Eberhard的灵活茎假说提出了相反的观点，即正是表型可塑性（以及她所谓的发育重组）促进了适应性辐射的茎系的快速进化和物种形成，形成了许多专门的、可塑性较低的物种，然后构成了适应性辐射。基于这一假说，发育可塑性被视为导致进化变化，即使在缺乏初始环境刺激的情况下，也会通过遗传同化以其他表型表现出来。在这里，我们从维多利亚湖和马拉维湖的适应性辐射和两个河流基系中精心挑选了四种具有代表性的丽鱼，并开始测试柔性茎假说（FSH）的预测。在东非的几个湖泊中，慈鲷鱼经历了爆炸性的适应性辐射，填补了大量的生态位，因此代表了检验这一假设的理想模型。在之前的工作和初步的实验中，我们可以根据喂给鱼的饲料的硬度（硬蜗牛和碎蜗牛），在分裂产卵中诱导出不同类型的牙齿和咽颌形态。在一种非地方性的河流慈鲷身上可能产生截然不同的摄食形态。根据FSH，我们预计从维多利亚湖和马拉维湖的适应性辐射中产生的两对特化和衍生物种的反应规范将小得多。在之前的RNA-seq实验和后来的工作中，我们发现了几组共表达基因，这些基因在颌骨向硬噬（咬蜗牛）颌骨转变的不同阶段都是活跃的。我们计划对所有六个物种进行饲养实验以及RNA-seq分析，这些分析将在已知的系统发育框架内进行分析和解释。我们预计，与FSH预测的两个基础物种相比，适应性辐射的四个衍生和特化地方性成员（年龄不同）在形态和转录方面的变化都要小。进一步的生物信息学分析将研究参与适应性表型反应的基因启动子的变异和变化，并与其他中性基因进行比较。

An organisms ability to adjust its phenotype in response to environmental stimuli is termed phenotypic plasticity. Traditionally it is often seen to hamper and constrain evolution. However, this view is debated and alternatively the flexible-stem hypothesis of West-Eberhard suggest the opposite, that exactly phenotypic plasticity (and what she calls developmental recombination) facilitates in stem lineages of adaptive radiations their rapid evolution and speciation into many specialized and less plastic species that then make up adaptive radiations. Based on this hypothesis developmental plasticity is seen to lead evolutionary change that later, even in lack of the initial environmental stimulus, is phenotypically expressed in alternative phenotypes through genetic assimilation. Here, we set out test the predictions of the flexible-stem hypothesis (FSH) in a set of four carefully chosen representative cichlid fish species from the adaptive radiations of Lake Victoria and Lake Malawi and two riverine basal lineages. Cichlid fishes have undergone explosive adaptive radiations in several East African lakes, filling a vast array of ecological niches, and thus represent an ideal model in which to test this hypothesis. In previous work and in preliminary experiments we could induce in split-broods different types of teeth and pharyngeal jaw morphologies based on the hardness of the diets that was fed to the fish (hard snails vs. crushed snails). It was possible to produce drastically different feeding morphologies in one of the non-endemic riverine cichlids. In accordance with the FSH we expect that the reaction norms will be much smaller in both of the two pairs of specialized and derived species from the adaptive radiations of Lakes Victoria and Malawi. In previous RNA-seq experiments and later work we identified several sets of co-expressed genes that were active during different phases of the jaw transformation towards a durophagous (snail-crushing) jaw. We plan to do conduct feeding-experiments with all six species as well as RNA-seq analyses that will be analyzed and interpreted within a known phylogenetic framework. We anticipate that both the variation in morphology as well as in transcriptional will be smaller in the four derived and specialized endemic members of the adaptive radiations (that are of different ages) than in the two basal species as would be predicted by the FSH. Further bioinformatics analyses will investigate variation and changes in promoters of genes involved in the adaptive phenotypic response and compared with other sets of neutral genes.