Saltini Marco, Barrett Spencer C H, Deinum Eva E
Mathematical and Statistical Methods (Biometris), Plant Science Group, Wageningen University, Wageningen, The Netherlands.
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
Evolution. 2024 Dec 22;79(1):65-79. doi: 10.1093/evolut/qpae140.
Mirror-image flowers (enantiostyly) involve a form of sexual asymmetry in which a flower's style is deflected either to the left or right side, with a pollinating anther orientated in the opposite direction. This curious floral polymorphism, which was known but not studied by Charles Darwin, occurs in at least 11 unrelated angiosperm families and represents a striking example of adaptive convergence in form and function associated with cross-pollination by insects. In several lineages, dimorphic enantiostyly (one stylar orientation per plant, both forms occurring within populations) has evolved from monomorphic enantiostyly, in which all plants can produce both style orientations. We use a modelling approach to investigate the emergence of dimorphic enantiostyly from monomorphic enantiostyly under gradual evolution. We show using adaptive dynamics that depending on the balance between inbreeding depression following geitonogamy, pollination efficiency, and plant density, dimorphism can evolve from an ancestral monomorphic population. In general, the newly emergent dimorphic population is stable against invasion of a monomorphic mutant. However, our model predicts that under certain ecological conditions, for example, a decline of pollinators, dimorphic enantiostyly may revert to a monomorphic state. We demonstrate using population genetics simulations that the observed evolutionary transitions are possible, assuming a plausible genetic architecture.
镜像花（花柱异长）涉及一种性不对称形式，即花的花柱偏向左侧或右侧，而授粉花药则朝向相反方向。这种奇特的花多态性，查尔斯·达尔文虽已知晓但未进行研究，至少在11个不相关的被子植物科中出现，是与昆虫异花授粉相关的形态和功能适应性趋同的显著例子。在几个谱系中，二型花柱异长（每株植物一种花柱方向，两种形式存在于种群中）是从单型花柱异长进化而来的，在单型花柱异长中，所有植物都能产生两种花柱方向。我们采用建模方法来研究在逐渐进化过程中从单型花柱异长出现二型花柱异长的情况。我们使用适应性动力学表明，根据同株异花授粉后的近亲繁殖衰退、授粉效率和植物密度之间的平衡，二型性可以从祖先的单型种群中进化出来。一般来说，新出现的二型种群对单型突变体的入侵是稳定的。然而，我们的模型预测，在某些生态条件下，例如传粉者数量下降，二型花柱异长可能会恢复到单型状态。我们使用群体遗传学模拟证明，假设一种合理的遗传结构，观察到的进化转变是可能的。
