Rice Sean H
Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, 06520.
Evolution. 1998 Jun;52(3):647-656. doi: 10.1111/j.1558-5646.1998.tb03690.x.
Evolution can change the developmental processes underlying a character without changing the average expression of the character itself. This sort of change must occur in both the evolution of canalization, in which a character becomes increasingly buffered against genetic or developmental variation, and in the phenomenon of closely related species that show similar adult phenotypes but different underlying developmental patterns. To study such phenomena, I develop a model that follows evolution on a surface representing adult phenotype as a function of underlying developmental characters. A contour on such a "phenotype landscape" is a set of states of developmental characters that produce the same adult phenotype. Epistasis induces curvature of this surface, and degree of canalization is represented by the slope along a contour. I first discuss the geometric properties of phenotype landscapes, relating epistasis to canalization. I then impose a fitness function on the phenotype and model evolution of developmental characters as a function of the fitness function and the local geometry of the surface. This model shows how canalization evolves as a population approaches an optimum phenotype. It further shows that under some circumstances, "decanalization" can occur, in which the expression of adult phenotype becomes increasingly sensitive to developmental variation. This process can cause very similar populations to diverge from one another developmentally even when their adult phenotypes experience identical selection regimes.
进化可以改变一个性状背后的发育过程，而不改变该性状本身的平均表现。这种变化必定会在稳态化的进化过程中发生，在此过程中，一个性状会越来越能抵御遗传或发育变异的影响；这种变化也必定会在亲缘关系密切的物种所呈现的现象中发生，这些物种具有相似的成年表型，但潜在的发育模式却不同。为了研究此类现象，我构建了一个模型，该模型在一个将成年表型表示为潜在发育性状函数的表面上追踪进化过程。在这样一个“表型景观”上的一条等高线是一组产生相同成年表型的发育性状状态。上位性会导致这个表面产生曲率，而稳态化程度则由沿着一条等高线的斜率来表示。我首先讨论表型景观的几何特性，将上位性与稳态化联系起来。然后我在表型上施加一个适应度函数，并将发育性状的进化建模为适应度函数和表面局部几何形状的函数。这个模型展示了随着种群接近最优表型，稳态化是如何进化的。它还进一步表明，在某些情况下，可能会发生“去稳态化”，即成年表型的表达对发育变异变得越来越敏感。即使它们的成年表型经历相同的选择机制，这个过程也会导致非常相似的种群在发育上彼此分化。
