Stone Judy L, Thomson James D
Department of Ecology and Evolution, State University of New York, Stony Brook, New York, 11794.
Evolution. 1994 Oct;48(5):1595-1606. doi: 10.1111/j.1558-5646.1994.tb02198.x.
A recent model by Lloyd and Webb derives conditions necessary for the evolution of distyly based on pollen-transfer probabilities between ancestral morphs and invading mutants. We used bumblebees visiting artificial flowers to measure the parameters of the model. Our findings supported the first evolutionary step proposed by the model, establishment of a stigma-height polymorphism. Conditions for the subsequent establishment of an anther-height polymorphism were not satisfied by pollen-transfer patterns alone. Because conditions for the first step are considered more onerous, however, and because the second stage depends on inbreeding depression as well as pollen-transfer patterns, we interpret our results as supporting the plausibility of the Lloyd-Webb model. Video images of bees visiting glass-sided artificial flowers demonstrate a mechanism for disassortative pollination between the ancestral and mutant morph. In general, pollen-transfer probabilities were negatively correlated with the height difference between anthers of the donor and stigma of the recipient. Style length affects bee feeding posture in such a way that disassortative pollination could feasibly occur in the absence of an anther-height polymorphism.
劳埃德和韦伯最近提出了一个模型，该模型基于祖先形态与入侵突变体之间的花粉转移概率，推导出了花柱异长进化所需的条件。我们利用访问人造花的大黄蜂来测量该模型的参数。我们的研究结果支持了该模型提出的第一步进化，即柱头高度多态性的建立。仅靠花粉转移模式，无法满足随后花药高度多态性建立的条件。然而，由于第一步的条件被认为更为苛刻，并且由于第二阶段既取决于近亲繁殖衰退，也取决于花粉转移模式，因此我们将研究结果解释为支持劳埃德 - 韦伯模型的合理性。访问玻璃壁人造花的蜜蜂的视频图像展示了祖先形态与突变形态之间的异花授粉机制。一般来说，花粉转移概率与供体花药和受体柱头之间的高度差呈负相关。花柱长度会影响蜜蜂的取食姿势，使得在没有花药高度多态性的情况下，异花授粉也有可能发生。
