Pinheiro Fabio, Cafasso Donata, Cozzolino Salvatore, Scopece Giovanni
Departamento de Botânica, Instituto de Biociências, Universidade Estadual Paulista, 13506-900, Rio Claro, SP, Brazil,
Università degli Studi di Napoli Federico II, Department of Biology, via Cinthia, I-80126, Naples, Italy and.
Ann Bot. 2015 Sep;116(3):457-67. doi: 10.1093/aob/mcv057. Epub 2015 May 7.
The evolution of interspecific reproductive barriers is crucial to understanding species evolution. This study examines the contribution of transitions between self-compatibility (SC) and self-incompatibility (SI) and genetic divergence in the evolution of reproductive barriers in Dendrobium, one of the largest orchid genera. Specifically, it investigates the evolution of pre- and postzygotic isolation and the effects of transitions between compatibility states on interspecific reproductive isolation within the genus.
The role of SC and SI changes in reproductive compatibility among species was examined using fruit set and seed viability data available in the literature from 86 species and ∼2500 hand pollinations. The evolution of SC and SI in Dendrobium species was investigated within a phylogenetic framework using internal transcribed spacer sequences available in GenBank.
Based on data from crossing experiments, estimations of genetic distance and the results of a literature survey, it was found that changes in SC and SI significantly influenced the compatibility between species in interspecific crosses. The number of fruits produced was significantly higher in crosses in which self-incompatible species acted as pollen donor for self-compatible species, following the SI × SC rule. Maximum likelihood and Bayesian tests did not reject transitions from SI to SC and from SC to SI across the Dendrobium phylogeny. In addition, postzygotic isolation (embryo mortality) was found to evolve gradually with genetic divergence, in agreement with previous results observed for other plant species, including orchids.
Transitions between SC and SI and the gradual accumulation of genetic incompatibilities affecting postzygotic isolation are important mechanisms preventing gene flow among Dendrobium species, and may constitute important evolutionary processes contributing to the high levels of species diversity in this tropical orchid group.
种间生殖隔离的演变对于理解物种进化至关重要。本研究探讨了自交亲和性（SC）与自交不亲和性（SI）之间的转变以及遗传分化在石斛属（最大的兰花属之一）生殖隔离进化中的作用。具体而言，研究了合子前隔离与合子后隔离的进化以及亲和性状态转变对该属种间生殖隔离的影响。
利用文献中86个物种的坐果率和种子活力数据以及约2500次人工授粉，研究SC和SI变化在物种间生殖亲和性中的作用。利用GenBank中可获得的内部转录间隔区序列，在系统发育框架内研究石斛属物种中SC和SI的进化。
基于杂交实验数据、遗传距离估计以及文献调查结果，发现SC和SI的变化显著影响种间杂交中物种间的亲和性。按照SI×SC规则，当自交不亲和物种作为花粉供体与自交亲和物种杂交时，产生的果实数量显著更高。最大似然法和贝叶斯检验并未拒绝在整个石斛属系统发育中从SI到SC以及从SC到SI的转变。此外，发现合子后隔离（胚胎死亡率）随着遗传分化而逐渐演变，这与之前对包括兰花在内的其他植物物种的观察结果一致。
SC和SI之间的转变以及影响合子后隔离的遗传不相容性的逐渐积累是阻止石斛属物种间基因流动的重要机制，可能构成了导致这个热带兰花类群高水平物种多样性的重要进化过程。
