Department of Biology, Rhodes College, Memphis, TN, 38112, USA.
Department of Biology, University of Rochester, Rochester, NY, 14627, USA.
Am J Bot. 2021 Feb;108(2):297-308. doi: 10.1002/ajb2.1605. Epub 2021 Feb 12.
Whole-genome duplication (polyploidy) is an important force shaping flowering-plant evolution. Ploidy-specific plant-pollinator interactions represent important community-level biotic interactions that can lead to nonrandom mating and the persistence of mixed-ploidy populations.
At a naturally occurring diploid-tetraploid contact zone of the autopolyploid desert shrub Larrea tridentata, we combined flower phenology analyses, collections of bees on plants of known cytotype, and flow cytometry analyses of bee-collected pollen loads to investigate whether (1) diploid and tetraploid plants have unique bee pollinator assemblages, (2) bee taxa exhibit ploidy-specific visitation and pollen collection biases, and (3) specialist and generalist bee taxa have ploidy-specific visitation and pollen collection biases.
Although bee assemblages overlapped, we found significant differences in bee visitation to co-occurring diploids and tetraploids, with the introduced honeybee (Apis mellifera) and one native species (Andrena species 12) more frequently visiting tetraploids. Consistent with bee assemblage differences, we found that diploid pollen was overrepresented among pollen loads on native bees, while pollen loads on A. mellifera did not deviate from the random expectation. However, mismatches between the ploidy of pollen loads and plants were common, consistent with ongoing intercytotype gene flow.
Our data are consistent with cytotype-specific bee visitation and suggest that pollinator behavior contributes to reduced diploid-tetraploid mating. Differences in bee visitation and pollen movement potentially contribute to an easing of minority cytotype exclusion and the facilitation of cytotype co-occurrence.
全基因组复制（多倍体）是塑造开花植物进化的重要力量。倍性特异性的植物-传粉者相互作用代表了重要的群落水平生物相互作用，可导致非随机交配和混合倍性种群的持续存在。
在 Larrea tridentata 自交多倍体荒漠灌木的自然发生的二倍体-四倍体接触区，我们结合花物候分析、对已知细胞型植物上的蜜蜂采集以及对蜜蜂采集的花粉负荷的流式细胞术分析，调查了以下问题：（1）二倍体和四倍体植物是否具有独特的蜜蜂传粉者组合；（2）蜜蜂类群是否表现出倍性特异性访问和花粉收集偏好；（3）专性和一般性蜜蜂类群是否具有倍性特异性访问和花粉收集偏好。
尽管蜜蜂类群重叠，但我们发现共同存在的二倍体和四倍体之间的蜜蜂访问存在显著差异，引入的蜜蜂（Apis mellifera）和一种本地物种（Andrena species 12）更频繁地访问四倍体。与蜜蜂组合差异一致，我们发现二倍体花粉在本地蜜蜂的花粉负荷中占优势，而 A. mellifera 的花粉负荷则没有偏离随机预期。然而，花粉负荷与植物之间的倍性不匹配很常见，这与持续的细胞间基因流一致。
我们的数据与倍性特异性的蜜蜂访问一致，并表明传粉者行为有助于减少二倍体-四倍体交配。蜜蜂访问和花粉运动的差异可能有助于减轻少数细胞型的排斥，并促进细胞型共存。
