Suissa Jacob S, Smith Makaleh
Department of Ecology and Evolutionary Biology, University of Tennessee Knoxville, Knoxville, TN, USA.
Environmental Studies Program, The New School, New York, NY, USA.
Evolution. 2025 Feb 3;79(2):164-175. doi: 10.1093/evolut/qpae159.
A contemporary interpretation of Dollo's Law states that the evolution of a specialized structure is irreversible. Among land plants, reproductive specialization shows a trend toward increasing complexity without reversion, raising questions about evolutionary steps and the irreversibility of reproductive complexity. Ferns exhibit varied reproductive strategies; some are dimorphic (producing separate leaves for photosynthesis and reproduction), while others are monomorphic (where one leaf is used for both photosynthesis and spore dispersal). This diversity provides an opportunity to examine the applicability of Dollo's Law in the evolution of reproductive leaf specialization. We analyzed 118 species in Blechnaceae and Onocleaceae, applying quantitative morphometrics and phylogenetic comparative methods to test the pillars of a modernized interpretation of Dollo's Law. The evolution of dimorphism in Blechnaceae is neither stepwise nor irreversible, with direct transitions from monomorphism to dimorphism, including several reversions. In contrast, Onocleaceae exhibits an irreversibility to monomorphism only upon further specialization of fertile leaves for humidity-driven spore dispersal; this suggests that additional specialization, not dimorphism alone, may facilitate irreversibility. These results provide insight into the canalization of fertile-sterile leaf dimorphism in seed plants, where the addition of traits like heterospory and integuments lead to further specialization and potential irreversibility. These findings suggest that as new specialized traits evolve alongside preexisting ones, reversion may become increasingly unlikely.
对多洛法则的当代解释认为，特殊结构的进化是不可逆的。在陆地植物中，繁殖特化呈现出一种朝着日益复杂发展且无逆转的趋势，这引发了关于进化步骤以及繁殖复杂性不可逆性的问题。蕨类植物展现出多样的繁殖策略；有些是二态的（产生用于光合作用和繁殖的不同叶片），而其他的则是单态的（其中一片叶子同时用于光合作用和孢子传播）。这种多样性为检验多洛法则在繁殖叶特化进化中的适用性提供了契机。我们分析了乌毛蕨科和球子蕨科的118个物种，运用定量形态计量学和系统发育比较方法来检验对多洛法则现代化解释的要点。乌毛蕨科中二态性的进化既不是逐步的也不是不可逆的，存在从单态直接转变为二态的情况，包括几次逆转。相比之下，球子蕨科只有在可育叶为湿度驱动的孢子传播进一步特化时才表现出向单态的不可逆性；这表明额外的特化，而非仅仅是二态性，可能促进不可逆性。这些结果为种子植物中可育 - 不育叶二态性的稳态化提供了见解，在种子植物中，诸如异型孢子和珠被等特征的增加导致了进一步的特化和潜在的不可逆性。这些发现表明，随着新的特殊性状与已有的性状一起进化，逆转可能越来越不可能发生。
