Data from: Preponderance of clonality triggers loss of sex in Bulbophyllum bicolor, an obligately outcrossing epiphytic orchid

Vegetative propagation (clonal growth) conveys several evolutionary advantages that positively affect life history fitness and is a widespread phenomenon among angiosperms that also reproduce sexually. However, a bias towards clonality can interfere with sexual reproduction and lead to sexual extinction, although a dearth of effective genetic tools and mathematical models for clonal plants has hampered assessment of these impacts. Using the endangered tropical epiphytic or lithophytic orchid Bulbophyllum bicolor as a model, we integrated an examination of breeding system with 12 microsatellite loci and models valid for clonal species to test for the ‘loss of sex’ and infer likely consequences for long-term reproductive dynamics. Bagging experiments and field observations revealed B. bicolor to be self-incompatible and pollinator-dependent, with an absence of fruit-set over four years. Challenging the assumptions that clonal populations can be as genotypically diverse as sexually reproducing ones and that clonality does not greatly influence genetic structure, just 22 multilocus genotypes were confirmed among all 15 extant natural populations, 12 of the populations were found to be monoclonal and all three multiclonal ones exhibited a distinct phalanx clonal architecture. Our results suggest that all B. bicolor populations depend overwhelmingly on clonal growth for persistence, with a concomitant loss of sex due to an absence of pollinators and a lack of mating opportunities at virtually all sites, both of which are further entrenched by habitat fragmentation. Such cryptic life history impacts, potentially contributing to extinction debt, could be widespread among similarly fragmented, outcrossing tropical epiphytes, demanding urgent conservation attention.

营养繁殖（克隆生长，Vegetative propagation）可赋予多种提升生活史适合度的进化优势，在同时进行有性繁殖的被子植物中广泛分布。然而，对克隆生长的过度依赖可能干扰有性生殖过程，最终导致有性繁殖灭绝，但目前针对克隆植物缺乏有效的遗传工具与数学模型，这极大阻碍了相关影响的评估工作。本研究以濒危热带附生/石生兰花二色卷瓣兰（Bulbophyllum bicolor）为模式物种，整合繁育系统检测、12个微卫星位点（microsatellite loci）分析以及适配克隆物种的模型，检验“有性繁殖丢失”假说，并推断其对种群长期生殖动态的潜在影响。套袋实验与野外观测结果显示，二色卷瓣兰为自交不亲和且依赖传粉者的物种，但在四年的观测周期内未观测到任何坐果事件。此前学界普遍假设克隆种群可拥有与有性繁殖种群相当的遗传多样性，且克隆生长不会显著改变种群遗传结构；但本研究结果表明，在现存的15个自然种群中仅确认了22个多位点基因型（multilocus genotypes），其中12个种群为单克隆种群，所有3个多克隆种群均呈现典型的集团式克隆架构（phalanx clonal architecture）。研究结果显示，二色卷瓣兰的所有种群几乎完全依赖克隆生长维持种群存续，同时由于传粉者缺失与几乎所有样地均缺乏交配机会，导致有性繁殖完全丢失，而生境破碎化进一步加剧了这一困境。这类隐蔽的生活史影响可能引发灭绝债务（extinction debt），在类似的破碎化异交热带附生植物类群中可能广泛存在，因此亟需开展针对性的保护工作。