The effects of ancestral plasticity and genetic assimilation on convergence and the diversification of East African cichlid fishes

不同的环境意味着不同的选择制度，从而预计影响健身。具有发育可塑性的适应性反应这种环境挑战的能力将有望增加生物体的生存机会。理论和实证研究表明，表型可塑性本身可以选择的目标，从而进化。表型可塑性已被证明在许多生态相关的性状，并应缓冲生物从自然选择。但它在物种形成和快速适应辐射过程中的作用还没有得到很好的理解和争议。“柔性茎模型”提出，表型可塑性可以促进谱系的多样化。由可塑性祖先启动的适应性辐射将导致表型多样性的突然增加，随后逐渐渠化为潜在的不同的先前可塑性表型，从而导致几个谱系具有不同的和较少的可塑性表型。这可能是通过降低环境敏感性的机制发生的，如遗传同化/渠化。当最初可塑性表达的表型经历遗传同化时，其可塑性将随之降低，性状的表型变得遗传固定，其遗传力增加。预计选择将更快地作用于这些表型，可能促进表型分化并加速物种形成。慈鲷鱼是一个很有前途的进化模式系统，在其中调查的一个灵活的干和遗传同化的谱系多样化和快速适应辐射的潜在贡献。慈鲷科的一个最有趣的关键创新，被认为是促进了他们的营养专业化程度，从而使他们无与伦比的多样化是他们的高度修改咽颚装置（PJA，一个功能性的第二颚，具有不同的表型塑料牙列，不断更换）。PJA的表型和牙齿的大小和形状在表型上是可塑的，特定的PJA形态反映了该物种的营养生态位。在这项研究中，我们专注于最关键的和最有争议的假设的灵活的茎：当不同的人群开始进行遗传同化，从而遗传固定的表型的时期。我们将探讨诱导可塑性的差异（通过分裂育雏饮食治疗常见的花园实验）之间的河流（祖先/源）和湖泊（专门/衍生）种群在几个慈鲷。我们将研究（通过RNAseq，qPCR和原位杂交）可塑性候选基因的潜在作用，其中一些我们已经获得。因为他们将表征在实验诱导的PJA形态的塑性反应期间的表达动力学和功能相关性。

Different environments mean different selective regimes and are thereby expected to affect fitness. The ability to respond adaptively with developmental plasticity to such environmental challenges would be expected to increase an organism’s chances to persist. Theoretical and empirical work suggests that phenotypic plasticity itself can be the target of selection and thus evolve. Phenotypic plasticity has been documented in many ecologically relevant traits and should buffer organisms from natural selection. But its role in speciation and during rapid adaptive radiations is not well understood and controversial. The "flexible stem model", proposes that phenotypic plasticity can boost a lineage’s diversification. An adaptive radiation initiated by a plastic ancestor would lead to a sudden increase in phenotypic diversity followed by a gradual canalization into potentially different formerly plastic phenotypes and thus lead to several lineages with then distinct and less plastic phenotypes. This might happen through mechanisms that reduce environmental sensitivity such as genetic assimilation/canalization. When an initially plastically expressed phenotype undergoes genetic assimilation, its plasticity would be concomitantly reduced, the trait’s phenotype becomes genetically fixed and its heritability increased. Selection would be expected act on these phenotypes faster, potentially promoting phenotypic divergence and speeding up speciation. Cichlid fishes are a promising evolutionary model systems in which to investigate the potential contributions of a flexible stem and genetic assimilation to lineage diversification and rapid adaptive radiations. One most interesting key innovation of cichlids that is thought to have facilitated their degree of trophic specializations and thereby permitting their un-rivalled diversification is their highly modified pharyngeal jaw apparatus (PJA, a functional second jaw with different phenotypically plastic dentition that gets replaced continuously). The phenotype of the PJA and the size and shape of the teeth are phenotypically plastic and a particular PJA morphology reflects the trophic niche of the species. In this study, we focus on the most crucial and most controversially debated assumption of the flexible stem: the period when divergent populations start to undergo genetic assimilation and thus genetic fixation of a phenotype. We will investigate differences in inducible plasticity (through split-brood diet treatments in common garden experiments) between riverine (ancestral/source) and lacustrine (specialized/derived) populations in several cichlids. We will investigate (through RNAseq, qPCR and in situ hybridization) the potential role of plasticity candidate genes, some of which we already obtained. For them will characterize the expression dynamics and functional relevance during the experimentally induced plastic response to the PJA morphology.