Palmer A R
Department of Biological Sciences, University of Alberta, Edmonton, Canada.
Proc Natl Acad Sci U S A. 1996 Dec 10;93(25):14279-86. doi: 10.1073/pnas.93.25.14279.
Phylogenetic analyses of asymmetry variation offer a powerful tool for exploring the interplay between ontogeny and evolution because (i) conspicuous asymmetries exist in many higher metazoans with widely varying modes of development, (ii) patterns of bilateral variation within species may identify genetically and environmentally triggered asymmetries, and (iii) asymmetries arising at different times during development may be more sensitive to internal cytoplasmic inhomogeneities compared to external environmental stimuli. Using four broadly comparable asymmetry states (symmetry, antisymmetry, dextral, and sinistral), and two stages at which asymmetry appears developmentally (larval and postlarval), I evaluated relations between ontogenetic and phylogenetic patterns of asymmetry variation. Among 140 inferred phylogenetic transitions between asymmetry states, recorded from 11 classes in five phyla, directional asymmetry (dextral or sinistral) evolved directly from symmetrical ancestors proportionally more frequently among larval asymmetries. In contrast, antisymmetry, either as an end state or as a transitional stage preceding directional asymmetry, was confined primarily to postlarval asymmetries. The ontogenetic origin of asymmetry thus significantly influences its subsequent evolution. Furthermore, because antisymmetry typically signals an environmentally triggered asymmetry, the phylogenetic transition from antisymmetry to directional asymmetry suggests that many cases of laterally fixed asymmetries evolved via genetic assimilation.
不对称性变异的系统发育分析为探索个体发育与进化之间的相互作用提供了一个强大的工具，因为：（i）许多具有广泛不同发育模式的高等后生动物中存在明显的不对称性；（ii）物种内的双侧变异模式可能识别出由基因和环境引发的不对称性；（iii）与外部环境刺激相比，发育过程中不同时间出现的不对称性可能对内部细胞质不均匀性更敏感。利用四种广泛可比的不对称状态（对称、反对称、右旋和左旋），以及不对称性在发育过程中出现的两个阶段（幼虫期和幼虫后期），我评估了不对称性变异的个体发育模式与系统发育模式之间的关系。在从五个门的11个纲记录的140个推断的不对称状态之间的系统发育转变中，在幼虫不对称中，方向性不对称（右旋或左旋）直接从对称祖先进化而来的比例更高。相比之下，反对称，无论是作为最终状态还是作为方向性不对称之前的过渡阶段，主要局限于幼虫后期的不对称。因此，不对称性的个体发育起源显著影响其随后的进化。此外，由于反对称通常表明是由环境引发的不对称，从反对称到方向性不对称的系统发育转变表明，许多侧向固定不对称的情况是通过遗传同化进化而来的。
