Galen Candace
Department of Biological Sciences, Bowling Green State University, Bowling Green, OH, 43403.
Evolution. 1989 Jul;43(4):882-890. doi: 10.1111/j.1558-5646.1989.tb05185.x.
Sweet-flowered plants of Polemonium viscosum in Colorado are visited by a fly-dominated pollinator fauna at timberline (krummholz), but almost exclusively by bumblebees in higher-elevation tundra habitats. Significant increases in flower size and height are associated with increasing elevation along this habitat gradient. This paper presents the results of an experiment designed to test whether bumblebees exert sufficient selection on morphometric floral phenotypes to account for the clinal shifts seen in natural populations. Two populations of sweet-flowered plants of krummholz origin were established: one randomly pollinated, the other solely bumblebee-pollinated. I tested the effects of two independent axes of floral variation, obtained by principal-components analysis, on mean seed set per flower of plants in each population. PC1, with strong correlations to corolla diameter, corolla length, and stem height, explained a significant amount of variance in seed set for bumblebee-pollinated plants but had no bearing on that of randomly pollinated plants. PC2, with strong correlation to flower number, did not influence seed set in either population. Bumblebee behavior was correlated with variation in PC1 scores of the selected population, yielding positive directional selection on morphometric floral traits associated with PC1. Selection coefficients for PC1, corolla length, corolla diameter, and inflorescence height were estimated, respectively, as 0.11, 0.09, 0.07, and 0.06 (P < 0.025 in all cases). These results support the hypothesis that pollinator-mediated selection can bring about changes in floral form, and can explain shifts in floral morphology of P. viscosum along natural habitat gradients.
科罗拉多州的粘叶花葱属甜花植物在树线（矮曲林）处主要由以苍蝇为主的传粉动物群访花，但在海拔较高的苔原栖息地几乎完全由大黄蜂访花。沿着这个栖息地梯度，花的大小和高度显著增加与海拔升高有关。本文介绍了一项实验的结果，该实验旨在测试大黄蜂是否对形态计量的花表型施加了足够的选择，以解释自然种群中观察到的渐变变化。建立了两个源自矮曲林的甜花植物种群：一个随机授粉，另一个仅由大黄蜂授粉。我测试了通过主成分分析获得的花变异的两个独立轴对每个种群中植物每朵花的平均结实率的影响。PC1与花冠直径、花冠长度和茎高密切相关，解释了大黄蜂授粉植物结实率的大量变异，但对随机授粉植物的结实率没有影响。PC2与花的数量密切相关，对两个种群的结实率均无影响。大黄蜂的行为与所选种群PC1得分的变异相关，对与PC1相关的形态计量花性状产生正向定向选择。PC1、花冠长度、花冠直径和花序高度的选择系数分别估计为0.11、0.09、0.07和0.06（所有情况下P < 0.025）。这些结果支持了传粉者介导的选择可以导致花形态变化的假设，并可以解释粘叶花葱属植物花形态沿自然栖息地梯度的变化。
