Department of Biological Sciences, University of Illinois at Chicago, 840 West Taylor Street MC067, Chicago, Illinois 60607, USA.
Evolution. 2012 Dec;66(12):3701-9. doi: 10.1111/j.1558-5646.2012.01730.x. Epub 2012 Aug 2.
Classic questions about trait evolution-including the directionality of character change and its interactions with lineage diversification-intersect in the study of plant breeding systems. Transitions from self-incompatibility to self-compatibility are frequent, and they may proceed within a species ("anagenetic" mode of breeding system change) or in conjunction with speciation events ("cladogenetic" mode of change). We apply a recently developed phylogenetic model to the nightshade family Solanaceae, quantifying the relative contributions of these two modes of evolution along with the tempo of breeding system change, speciation, and extinction. We find that self-incompatibility, a genetic mechanism that prevents self-fertilization, is lost largely by the cladogenetic mode. Self-compatible species are thus more likely to arise from the isolation of a newly self-compatible population than from species-wide fixation of self-compatible mutants. Shared polymorphism at the locus that governs self-incompatibility shows it to be ancestral and not regained within this family. We demonstrate that failing to account for cladogenetic character change misleads phylogenetic tests of evolutionary irreversibility, both for breeding system in Solanaceae and on simulated trees.
经典的性状进化问题，包括性状变化的方向性及其与谱系多样化的相互作用，在植物繁育系统的研究中交汇在一起。自交不亲和性向自交亲和性的转变很常见，它们可能在一个物种内发生（“渐成性”的繁育系统变化模式），也可能与物种形成事件同时发生（“分生性”的变化模式）。我们将最近开发的系统发育模型应用于茄科植物，定量分析了这两种进化模式以及繁育系统变化、物种形成和灭绝的速度的相对贡献。我们发现，自交不亲和性是一种阻止自花授粉的遗传机制，主要通过分生性模式丢失。因此，自交亲和种更有可能是由一个新的自交亲和群体的隔离而不是由整个物种范围内自交亲和突变体的固定产生的。控制自交不亲和性的基因座的共享多态性表明它是祖先的，而不是在这个家族中重新获得的。我们证明，如果不考虑分生性特征变化，那么对于茄科植物和模拟树的繁育系统，对进化不可逆性的系统发育测试都会产生误导。
