Phenotypic evolution can cause either divergent or convergent phenotypic patterns. Even adaptation to the same environment may result in divergence of some elements of phenotype, whereas for other morphological traits it could cause phenotypic convergence. We hypothesize that at least some phenotypic characters diverge monotonically, hence they evolve irreversibly even in very closely related species, and this happens in spite of multiple convergent adaptive patterns. We studied the evolution of phenotype in 13 closely related Caucasian rock lizards (Darevskia), whose phylogenetic relationships are well known. We used head shape and the outlines of three important scales, using geometric morphometrics. We studied the association of the overall head shape, individual principal components of head shape and scale outlines with four predictors: phylogeny, habitat, sex and size. The overall head shape was not correlated with any of these predictors, whereas some principal components were correlated with habitat or phylogeny. Habitat type explained the highest fraction of variation in head shape and anal scale area. The relatedness inferred from the components of phenotype not correlated with habitat was congruent with the phylogenetic tree inferred from molecular data. Although adaptation to local environments may obscure the phylogenetic signal present in phenotype, there are components of phenotype whose evolution is irreversible.

中文翻译：

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高加索岩蜥（Darevskia）的表型发散，收敛和演化

表型演变可能导致发散或趋同的表型模式。即使适应相同的环境，也可能导致某些表型元素发生分歧，而对于其他形态特征，可能会导致表型趋同。我们假设至少有一些表型特征单调发散，因此即使在密切相关的物种中它们也不可逆地进化，尽管有多种会聚的适应性模式，但这种情况还是会发生。我们研究了13种密切相关的高加索岩蜥（Darevskia）的表型演变），其系统发育关系是众所周知的。我们使用头部形态和三个重要比例尺的轮廓，并使用了几何形态计量学。我们研究了整体头部形状，头部形状和比例轮廓的各个主要组成部分与四个预测因子的关系：系统发育，栖息地，性别和大小。总体头部形状与这些预测指标均不相关，而某些主要成分与栖息地或系统发育相关。栖息地类型解释了头部形状和肛门垢面积变化的最大部分。从表型成分推断出的与栖息地无关的相关性与从分子数据推断出的系统发育树是一致的。尽管适应当地环境可能会掩盖表型中存在的系统发生信号，