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，clonal growth）可带来多项正向影响生活史适合度的进化优势，且在兼具有性生殖的被子植物中广泛分布。然而，对克隆生长的偏好会干扰有性生殖并可能导致有性生殖灭绝，但由于缺乏针对克隆植物的有效遗传工具与数学模型，相关影响的评估工作长期受阻。本研究以濒危热带附生或石生兰科植物双色石豆兰（Bulbophyllum bicolor）为模式物种，将繁育系统（breeding system）调查与12个微卫星位点（microsatellite loci）分析及适用于克隆物种的模型相结合，用以检验‘有性生殖丧失’现象，并推测其对长期生殖动态的潜在影响。套袋实验与野外观测结果显示，双色石豆兰自交不亲和（self-incompatible）且依赖传粉者（pollinator-dependent），但连续四年均未坐果（fruit-set）。本研究挑战了两项既有假设：一是克隆种群的基因型多样性可与有性生殖种群持平，二是克隆生长不会显著影响种群遗传结构。结果显示，在全部15个现存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（monoclonal），剩余3个多克隆种群（multiclonal）均呈现出典型的密集型克隆构型（phalanx clonal architecture）。研究结果表明，双色石豆兰的所有种群几乎完全依赖克隆生长维持存续，同时由于几乎所有样地均缺乏传粉者与交配机会，导致有性生殖丧失，而生境破碎化进一步加剧了这一问题。这类隐蔽的生活史影响可能加剧灭绝债务（extinction debt），在同样经历生境破碎化的异交（outcrossing）热带附生植物中可能广泛存在，因此亟需引起保护生物学界的重视。