Understanding the mechanisms of adaptive population differentiation requires that both the functional and adaptive significance of divergent traits are characterized in contrasting environments. Here, we (a) determined the effects of floral spur length on pollen removal and receipt using plants with artificial spurs representing the species‐wide variation in length, and (b) quantified pollinator‐mediated selection on spur length and three traits contributing to floral display in two populations each of the short‐spurred and the long‐spurred ecotype of the orchid Platanthera bifolia. Both pollen receipt and removal reached a maximum at 28–29 mm long spurs in a short‐spurred population visited by short‐tongued moths. In contrast, pollen receipt increased linearly across the tested range (4–52 mm) and pollen removal was unrelated to spur length in a long‐spurred population predominantly visited by a long‐tongued moth. The experimentally documented effects on pollen transfer were not reflected in pollinator‐mediated selection through female fitness or pollen removal indicating that the natural within‐population variation in spur length was insufficient to result in detectable variation in pollen limitation. Our study illustrates how combining trait manipulation with analysis of causes and strength of phenotypic selection can illuminate the functional and adaptive significance of trait expression when trait variation is limited.

中文翻译：

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性状表达和授粉方式的操纵揭示了支线长度的适应性意义

了解适应性种群分化的机制需要在对比环境中表征不同特征的功能和适应性意义。在这里，我们 (a) 使用具有代表物种范围内长度变化的人工刺的植物确定了花刺长度对花粉去除和接收的影响，以及 (b) 量化传粉媒介介导的对刺长度和有助于花的三个性状的选择。在两个种群中分别展示了双叶兰 Platanthera 的短刺和长刺生态型。在短舌蛾访问的短刺种群中，花粉的接收和去除均在 28-29 毫米长的刺中达到最大值。相比之下，在测试范围内（4-52 毫米），花粉接收呈线性增加，并且花粉去除与主要由长舌蛾访问的长刺种群中的刺长无关。实验记录的对花粉转移的影响并未反映在通过雌性适应性或花粉去除进行的传粉媒介介导的选择中，这表明种群内部的自然变异不足以导致花粉限制的可检测变化。我们的研究说明了如何将性状操纵与表型选择的原因和强度分析相结合，可以阐明当性状变异有限时性状表达的功能和适应性意义。实验记录的对花粉转移的影响并未反映在通过雌性适应度或花粉去除进行的传粉媒介介导的选择中，这表明种群内自然的支链长度变化不足以导致花粉限制的可检测变化。我们的研究说明了如何将性状操纵与表型选择的原因和强度分析相结合，可以阐明当性状变异有限时性状表达的功能和适应性意义。实验记录的对花粉转移的影响并未反映在通过雌性适应性或花粉去除进行的传粉媒介介导的选择中，这表明种群内部的自然变异不足以导致花粉限制的可检测变化。我们的研究说明了如何将性状操纵与表型选择的原因和强度分析相结合，可以阐明当性状变异有限时性状表达的功能和适应性意义。