Data from: Higher seed number compensates for lower fruit set in deceptive orchids

1. Floral deception is widespread in orchids, with more than one third of the species being pollinated this way. The evolutionary success of deceptive orchids is puzzling, as species employing this strategy are thought to have low reproductive success (less flowers yielding fruits) because of low pollination rates. However, direct measurements of total seed production in orchids – which is a better measure of reproductive success – are scarce due to the extremely small size of their seeds. 2. Here, we quantified seed numbers in 1,015 fruits belonging to 48 orchid species from the Pannonian ecoregion (central Europe) and obtained fruit-set and thousand-seed weight data for these species from the literature. We used phylogenetic comparative methods to test the hypothesis that deceptive species should compensate for their lower fruit-set by having either more flowers, larger seeds or more seeds in a fruit. 3. Similarly to previous studies, we found that deceptive orchids have substantially lower fruits-set than nectar-rewarding ones. Also, we found that deceptive species have more seeds in a fruit but not more flowers or larger seeds compared to nectar-rewarding ones. Based on our results, deceptive species compensate for their lower fruit-set by having higher seed numbers per fruit. As a consequence, their seed numbers per shoot do not differ from that of nectar-rewarding ones. 4. Together with other benefits of deceptive pollination (e.g. lower energy expenditure due to the lack of nectar production and higher genetic variability due to decreased probability of geitonogamous pollination), our results can explain why deceptive strategies are so widespread in the orchid family. 5. Synthesis. Our results indicate that deceptive orchids can compensate for their lower fruit-set by having more (but not larger) seeds in a fruit than rewarding species. These findings highlight possible ways in which plants can increase their reproductive success in face of pollinator limitation. We emphasize that fruit-set in itself is an inappropriate measure of the reproductive success of orchids – the total number of seeds per shoot is a much better approximation.

1. 兰科植物中花欺骗传粉策略极为普遍，超过三分之一的兰花物种通过该方式完成传粉。欺骗性兰科植物的演化成功长期以来令人困惑：由于传粉效率低下，采用该策略的物种被认为繁殖成功率偏低（即坐果花朵占比更低）。然而，兰花种子体型极小，导致针对其总种子产量——这一更能反映繁殖成功率的指标——的直接测量数据仍极为匮乏。
2. 本研究针对潘诺尼亚生态区（中欧）的48个兰花物种的1015个果实开展种子数量定量统计，并从已发表文献中获取了这些物种的坐果率与千粒重数据。我们采用系统发育比较法（phylogenetic comparative methods）检验如下假说：欺骗性兰花物种可通过增加单花数量、增大种子体积或提升单果种子数，来弥补其较低的坐果率。
3. 与既往研究结果一致，我们发现欺骗性兰花的坐果率显著低于产蜜奖励型兰花。同时，相较于产蜜奖励型物种，欺骗性兰花的单果种子数更多，但单花数量与种子体积并无显著差异。基于本研究结果，欺骗性兰花可通过提升单果种子数弥补其较低的坐果率，因此其每花枝的总种子数与产蜜奖励型物种并无显著差异。
4. 结合欺骗性传粉策略的其他优势（例如：无需分泌花蜜以降低能量消耗，以及因同株异花传粉概率降低而提升种群遗传多样性），本研究结果可解释为何欺骗性传粉策略在兰科植物中如此普遍。
5. 综合讨论。本研究结果表明，相较于产蜜奖励型兰花，欺骗性兰花可通过增加单果种子数（而非增大种子体积）弥补其较低的坐果率。这些发现揭示了植物在传粉者受限条件下提升繁殖成功率的潜在途径。我们着重指出，坐果率本身并非衡量兰花繁殖成功率的恰当指标——单花枝总种子数才是更为合适的评估近似值。