Gibert Jean-Michel
Sorbonne Universités, UPMC Université Paris 06, CNRS, Biologie du Développement Paris Seine, Institut de Biologie Paris Seine (LBD-IBPS), 75005, Paris, France.
Dev Genes Evol. 2017 Sep;227(5):297-307. doi: 10.1007/s00427-017-0589-0. Epub 2017 Aug 6.
Phenotypic plasticity, the ability of a given genotype to produce different phenotypes in response to distinct environmental conditions, is widely observed in the wild. It is believed to facilitate evolution and, under the "flexible stem hypothesis", it is thought that an ancestral plastic species can be at the origin of sister lineages with divergent phenotypes fixed by genetic assimilation of alternative morphs. We review here the genetic mechanisms underlying such phenomenon. We show several examples in which the same gene shows transcriptional plasticity in response to environmental factors and divergence of expression within or between species. Thus, the same gene is involved both in the plasticity of a trait and in the evolution of that trait. In a few cases, it can be traced down to cis-regulatory variation in this gene and, in one case, in the very same regulatory sequence whose activity is modulated by the environment. These data are compatible with the "flexible stem hypothesis" and also suggest that the evolution of the plasticity of a trait and the evolution of the trait are not completely uncoupled as they often involve the same locus. Furthermore, the "flexible stem hypothesis" implies that it is possible to canalize initially plastic phenotypes. Several studies have shown that it was possible through modification of chromatin regulation or hormonal signalling/response. Further studies of phenotypic plasticity in an evolutionary framework are needed to see how much the findings described in this review can be generalized.
表型可塑性是指给定基因型在不同环境条件下产生不同表型的能力，在自然界中广泛存在。人们认为它有助于进化，并且在“灵活主干假说”下，有人认为一个祖先可塑性物种可能是姐妹谱系的起源，这些谱系具有通过替代形态的遗传同化而固定下来的不同表型。我们在此回顾这种现象背后的遗传机制。我们展示了几个例子，其中同一个基因对环境因素表现出转录可塑性，并且在物种内部或物种之间存在表达差异。因此，同一个基因既参与了性状的可塑性，也参与了该性状的进化。在少数情况下，可以追溯到该基因的顺式调控变异，在一个案例中，甚至可以追溯到其活性受环境调节的同一调控序列。这些数据与“灵活主干假说”相符，也表明性状可塑性的进化和性状的进化并非完全不相关，因为它们通常涉及相同的基因座。此外，“灵活主干假说”意味着有可能使最初具有可塑性的表型变得稳定。几项研究表明，通过改变染色质调控或激素信号传导/反应是有可能的。需要在进化框架内对表型可塑性进行进一步研究，以了解本综述中描述的发现能够在多大程度上得到推广。
