Gunter Helen M, Schneider Ralf F, Karner Immanuel, Sturmbauer Christian, Meyer Axel
Lehrstuhl für Zoologie und Evolutionsbiologie, Department of Biology, University of Konstanz, Konstanz, Germany.
Zukunftskolleg, University of Konstanz, Konstanz, Germany.
Mol Ecol. 2017 Dec;26(23):6634-6653. doi: 10.1111/mec.14405. Epub 2017 Nov 23.
Adaptive radiations are characterized by adaptive diversification intertwined with rapid speciation within a lineage resulting in many ecologically specialized, phenotypically diverse species. It has been proposed that adaptive radiations can originate from ancestral lineages with pronounced phenotypic plasticity in adaptive traits, facilitating ecologically driven phenotypic diversification that is ultimately fixed through genetic assimilation of gene regulatory regions. This study aimed to investigate how phenotypic plasticity is reflected in gene expression patterns in the trophic apparatus of several lineages of East African cichlid fishes, and whether the observed patterns support genetic assimilation. This investigation used a split brood experimental design to compare adaptive plasticity in species from within and outside of adaptive radiations. The plastic response was induced in the crushing pharyngeal jaws through feeding individuals either a hard or soft diet. We find that nonradiating, basal lineages show higher levels of adaptive morphological plasticity than the derived, radiated lineages, suggesting that these differences have become partially genetically fixed during the formation of the adaptive radiations. Two candidate genes that may have undergone genetic assimilation, gif and alas1, were identified, in addition to alterations in the wiring of LPJ patterning networks. Taken together, our results suggest that genetic assimilation may have dampened the inducibility of plasticity related genes during the adaptive radiations of East African cichlids, flattening the reaction norms and canalizing their feeding phenotypes, driving adaptation to progressively more narrow ecological niches.
适应性辐射的特征是适应性多样化与谱系内的快速物种形成相互交织，从而产生许多生态上特化、表型多样的物种。有人提出，适应性辐射可能起源于在适应性性状上具有明显表型可塑性的祖先谱系，促进了生态驱动的表型多样化，最终通过基因调控区域的遗传同化而固定下来。本研究旨在调查表型可塑性如何在东非丽鱼科鱼类几个谱系的营养器官的基因表达模式中体现，以及观察到的模式是否支持遗传同化。这项调查采用了分窝实验设计，以比较适应性辐射内外物种的适应性可塑性。通过给个体喂食硬或软的食物，在碾碎型咽颌中诱导可塑性反应。我们发现，非辐射的基部谱系比衍生的辐射谱系表现出更高水平的适应性形态可塑性，这表明这些差异在适应性辐射形成过程中已部分地在基因上固定下来。除了LPJ模式网络的布线改变外，还鉴定了两个可能经历了遗传同化的候选基因，即gif和alas1。综上所述，我们的结果表明，在东非丽鱼科鱼类的适应性辐射过程中，遗传同化可能削弱了可塑性相关基因的诱导性，使反应规范变平并使它们的摄食表型趋于稳定，从而推动它们适应越来越狭窄的生态位。
