Husband Brian C, Barrett Spencer C H
Department of Botany, University of Toronto, M5S 3B2, Toronto, Ontario, Canada.
Oecologia. 1992 Mar;89(3):365-371. doi: 10.1007/BF00317414.
The frequencies of floral morphs in populations of tristylous Eichhornia paniculata often deviate from the theoretical expectation of equality. This variation is associated with the breakdown of tristyly and the evolution of self-fertilization. Differences in morph frequencies could result from selection pressures due to variable levels of insect visitation to populations and contrasting foraging behavior among the floral morphs. We estimated pollinator densities in 16 populations and quantified visitation sequences to morphs in five populations of E. paniculata in northeastern Brazil. Foraging behavior among floral morphs was measured as the frequency of visits to morphs relative to their frequency in the population (preference) and number of flights between inflorescences of the same versus different morphs (constancy). Pollinator density (number/m/minute) was not correlated with population size, plant density or morph diversity. Pollinator densities varied most among populations of less than 200 plants. Whether pollinators discriminated among the morphs, depended on whether they primarily collected nectar or pollen. In four populations, nectar-feeding bees (Ancyloscelis and Florilegus spp.) and butterflies showed no consistent preference or constancy among the morphs. In contrast, pollen-collecting bees (Trigona sp.) visited a lower proportion of longstyled inflorescences than expected and tended to visit more mid-and short-styled inflorescences in succession, once they were encountered. Pollinator constancy for morphs did not result from differences in inflorescence production or spatial patchiness among the morphs. Although non-random pollinator visitation to morphs in heterostylous populations could potentially affect mating and hence morph frequencies, the observed visitation patterns in this study do not provide evidence that pollinators play a major role in influencing floral morph frequencies.
三型花柱的穗花狐尾藻种群中花形态的频率常常偏离理论上的相等预期。这种变异与三型花柱的瓦解和自花受精的进化有关。花形态频率的差异可能是由于昆虫对不同种群的访问水平不同以及花形态之间觅食行为的差异所导致的选择压力造成的。我们估计了16个种群中的传粉者密度，并对巴西东北部5个穗花狐尾藻种群中花形态的访问顺序进行了量化。花形态之间的觅食行为通过相对于其在种群中的频率（偏好）的访问频率以及相同形态与不同形态的花序之间的飞行次数（专一性）来衡量。传粉者密度（只/分钟）与种群大小、植物密度或形态多样性无关。传粉者密度在植物数量少于200株的种群中变化最大。传粉者是否对不同形态有区分，取决于它们主要采集花蜜还是花粉。在4个种群中，取食花蜜的蜜蜂（Ancyloscelis和Florilegus属）和蝴蝶在不同形态之间没有表现出一致的偏好或专一性。相比之下，采集花粉的蜜蜂（Trigona属）访问长花柱花序的比例低于预期，并且一旦遇到中花柱和短花柱花序，往往会连续访问更多。传粉者对形态的专一性并非源于不同形态之间花序产量或空间分布的差异。尽管在异型花柱种群中传粉者对形态的非随机访问可能会潜在地影响交配，进而影响形态频率，但本研究中观察到的访问模式并未提供证据表明传粉者在影响花形态频率方面起主要作用。
