Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Sevilla, Spain.
Department of Biological Sciences, University of Cape Town, Cape Town, South Africa.
Plant Biol (Stuttg). 2018 Jan;20 Suppl 1:100-111. doi: 10.1111/plb.12670.
Heterostyly is a sex polymorphism that has challenged evolutionary biologists ever since Darwin. One of the lineages where heterostyly and related stylar conditions appear more frequently is Linum (Linaceae). This group is particularly suitable for testing competing hypotheses about ancestral and transitional stages on the evolutionary building up of heterostyly. We generated a phylogeny of Linum based on extensive sampling and plastid and nuclear DNA sequences, and used it to trace the evolution of character states of style polymorphism. We also revised available data on pollination, breeding systems, and polyploidy to analyse their associations. Our results supported former phylogenetic hypotheses: the paraphyly of Linum and the non-monophyly of current taxonomic sections. Heterostyly was common in the genus, but appeared concentrated in the Mediterranean Basin and the South African Cape. Ancestral character state reconstruction failed to determine a unique state as the most probable condition for style polymorphism in the genus. In contrast, approach herkogamy was resolved as ancestral state in some clades, giving support to recent hypotheses. Some traits putatively related to heterostyly, such as life history and polyploidy, did show marginal or non-significant phylogenetic correlation, respectively. Although pollinator data are limited, we suggest that beeflies are associated with specific cases of heterostyly. The consistent association between style polymorphism and heteromorphic incompatibility points to ecological factors as drivers of the multiple evolution of style polymorphism in Linum. Albeit based on limited evidence, we hypothesised that specialised pollinators and lack of mating opportunities drive evolution of style polymorphism and loss of the polymorphism, respectively.
异型花柱是一种性多态现象，自达尔文以来一直困扰着进化生物学家。在异型花柱和相关花柱条件出现更为频繁的谱系中，有一种是亚麻属（亚麻科）。该类群特别适合检验关于异型花柱进化构建的祖先和过渡阶段的竞争假说。我们基于广泛的采样和质体及核 DNA 序列生成了亚麻属的系统发育，并利用它来追踪花柱多态性特征状态的进化。我们还修订了有关授粉、繁殖系统和多倍体的数据，以分析它们的关联。我们的结果支持了以前的系统发育假说：亚麻属的并系和当前分类群的非单系性。异型花柱在属中很常见，但主要集中在地中海盆地和南非海角。祖先特征状态重建未能确定单一状态作为属中花柱多态性最可能的条件。相比之下，在一些分支中，雌雄蕊异长被解析为祖先状态，这为最近的假说提供了支持。一些与异型花柱相关的特征，如花史和多倍体，分别显示出边缘或非显著的系统发育相关性。尽管授粉者的数据有限，但我们认为大黄蜂与异型花柱的特定案例有关。花柱多态性和异型不亲和之间的一致关联表明，生态因素是亚麻属中花柱多态性多次进化的驱动因素。尽管基于有限的证据，但我们假设专门的授粉者和缺乏交配机会分别推动了花柱多态性的进化和多态性的丧失。
