Recurrent evolution of dioecy in bryophytes

The origin and maintenance of separate sexes (dioecy) is an enduring evolutionary puzzle. Although both hermaphroditism and dioecy occur in many diverse clades, we know little about the long-term evolutionary consequences of changing sexual system. Here we find evidence for at least 133 transitions between sexual systems in mosses, representing an almost unparalleled lability in the evolution of their sexual systems. Furthermore, in contrast to predictions, the transition rate from hermaphroditism to dioecy was approximately twice as high as the reverse transition. Our results also suggest that hermaphodites may have higher rates of diversification than dioecious mosses. These results illustrate the utility of mosses for understanding the genomic and macroevolutionary consequences of hermaphroditism and dioecy.雌雄异株（dioecy）的起源与维持机制一直是进化生物学领域长期存在的未解难题。尽管雌雄同体（hermaphroditism）与雌雄异株在众多演化支系中均有分布，但学界对改变性别系统所带来的长期演化后果仍知之甚少。本研究在苔藓植物中发现了至少133次性别系统转换的证据，表明其性别系统的演化可塑性近乎无与伦比。此外，与此前的理论预测相悖，从雌雄同体向雌雄异株的转换速率约为反向转换的两倍。本研究结果还显示，雌雄同体苔藓植物的物种分化速率可能高于雌雄异株类群。上述研究结果充分彰显了苔藓植物作为研究模型，在解析雌雄同体与雌雄异株的基因组演化及宏观演化后果方面的重要价值。