Trevizan R, Oliveira P E, Brito V L G, Oliveira L, Telles F
Programa de Pós-Graduação em Biologia Vegetal, Universidade Estadual de Campinas, Campinas, Brazil.
Programa de Pós-Graduação em Ecologia, Conservação e Manejo da Fauna Silvestre, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Plant Biol (Stuttg). 2025 Jul 28. doi: 10.1111/plb.70079.
Plants can use non-floral signals to advertise the presence of resources to pollinators. The distylous Psychotria poeppigiana (Rubiaceae) has reddish bracts with small yellow flowers. Similar to other bracted plants with inconspicuous flowers, such bracts may signal the presence of nectar to pollinators. We investigated whether bracts act as honest signals in P. poeppigiana and how variation in bract traits affects floral reward and fructification. We asked: (1) Is there a relation between attractive traits (i.e. bracts and flowers) and the availability (quantity) and quality of the resource offered? (2) Do bract traits influence fructification rate? We hypothesized that bracts act as an honest signal to pollinators, being positively associated with nectar quantity and quality. If the signal is honest, we also expected that bracts with more resources could potentially attract more visits and result in a higher fruit set. We tested: (1) bract and flower trait differences between long-styled (L-styled) and short-styled (S-styled) morphs; (2) the relationship between bract (size, shape, asymmetry, and colour) and flower (length and diameter) traits and floral resource availability and quality; (3) bract trait effect on fruit set; and (4) whether bract size influences the total number of flowers and bract mortality. Larger bracts were positively associated with nectar volume, number of flowers, and increased bract mortality. In contrast, smaller bracts were linked to higher fruit set. Bract colour and asymmetry had no significant effect on resource production or fruit set. We additionally found differences between morphs: the S-morph had larger bracts (10.37%), longer flowers (13.67%), and more flowers per bract (22%) than the L-morph. We conclude that bracts in P. poeppigiana act as an honest signal to pollinators, as larger bracts produced more nectar. The higher fruit set in smaller bracts and increased mortality in larger ones suggest a potential division of reproductive roles, with S-styled (larger bracts) flowers contributing to male reproductive function and L-styled (smaller bracts) to female function.
植物可以利用非花部信号向传粉者宣传资源的存在。二型花柱的波氏九节（茜草科）有带小红苞片的小黄花。与其他具苞片且花不显眼的植物类似，这样的苞片可能向传粉者暗示花蜜的存在。我们研究了在波氏九节中苞片是否作为诚实信号，以及苞片性状的变异如何影响花部报酬和结实情况。我们提出以下问题：（1）吸引性状（即苞片和花）与所提供资源的可利用性（数量）和质量之间是否存在关联？（2）苞片性状是否影响结实率？我们假设苞片对传粉者起到诚实信号的作用，与花蜜数量和质量呈正相关。如果该信号是诚实的，我们还预期具有更多资源的苞片可能吸引更多访花者并导致更高的坐果率。我们进行了以下测试：（1）长花柱型（L型）和短花柱型（S型）形态之间的苞片和花性状差异；（2）苞片（大小、形状、不对称性和颜色）与花（长度和直径）性状与花部资源可利用性和质量之间的关系；（3）苞片性状对坐果的影响；（4）苞片大小是否影响花的总数和苞片死亡率。更大的苞片与花蜜量、花的数量以及苞片死亡率增加呈正相关。相比之下，更小的苞片与更高的坐果率相关。苞片颜色和不对称性对资源产出或坐果没有显著影响。我们还发现了不同形态之间的差异：S型形态的苞片更大（10.37%）、花更长（13.67%）且每个苞片上的花更多（22%），比L型形态的多。我们得出结论，波氏九节中的苞片对传粉者起到诚实信号的作用，因为更大的苞片产生更多花蜜。更小苞片的更高坐果率以及更大苞片的死亡率增加表明了一种潜在的生殖角色分工，S型（更大苞片）花有助于雄性生殖功能，而L型（更小苞片）花有助于雌性生殖功能。
