Department of Biology and School of Earth, Environmental and Marine Sciences, University of Texas Rio Grande Valley, Edinburg, TX, USA.
Intercollege Graduate Degree Program in Ecology, The Pennsylvania State University, University Park, Pennsylvania, 16802, USA.
Am J Bot. 2021 Jan;108(1):74-82. doi: 10.1002/ajb2.1594. Epub 2021 Jan 15.
Inbreeding depression is well documented in flowering plants and adversely affects a wide range of fitness-related traits. Recent work has begun to explore the effects of inbreeding on ecological interactions among plants and other organisms, including insect herbivores and pathogens. However, the effects of inbreeding on floral traits, floral scents, and pollinator visitation are less well studied.
Using inbred and outbred maternal families of horsenettle (Solanum carolinense, Solanaceae), we examined the effects of inbreeding on traits associated with pollinator attraction and floral rewards. Specifically, we measured corolla size, counted pollen grains per flower, and analyzed floral volatile emissions via gas chromatography and mass spectrometry. We also examined pollinator visitation to experimental arrays of flowering inbred and outbred plants under field conditions.
Compared to those of outbred plants, flowers of inbred plants exhibited reduced corolla size and pollen production, as well as significantly reduced emission of the two most abundant volatile compounds in the floral blend. Furthermore, bumblebees-the main pollinators of horsenettle-discriminated against inbred flowers in the field: bees were more likely to make initial visits to flowers on outbred plants, visited outbred flowers more often overall, and spent more time on outbred flowers.
These results show that inbreeding can (1) alter floral traits that are known to mediate pollinator attraction; (2) reduce the production of floral rewards (pollen is the sole reward in horsenettle); and (3) adversely affect pollinator visitation under field conditions.
近亲繁殖衰退在开花植物中已有充分记录，并对广泛的与适应度相关的特征产生不利影响。最近的研究开始探索近亲繁殖对植物与其他生物（包括昆虫食草动物和病原体）之间生态相互作用的影响。然而，近亲繁殖对花部特征、花的气味和传粉者访问的影响研究较少。
我们使用曼陀罗（Solanum carolinense，茄科）的自交和杂交母系家系，研究了近亲繁殖对与传粉者吸引和花部报酬相关的特征的影响。具体来说，我们测量了花被大小、每朵花的花粉粒数，并通过气相色谱和质谱分析了花的挥发性排放物。我们还在野外条件下，检查了实验性的开花自交和杂交植物群体中传粉者的访问情况。
与杂交植物的花朵相比，自交植物的花朵表现出花被尺寸和花粉产量减小，以及花部混合物中两种最丰富的挥发性化合物的排放显著减少。此外，熊蜂（曼陀罗的主要传粉者）在野外对自交花朵有歧视：蜜蜂更有可能首先访问杂交植物的花朵，总体上访问杂交花朵的次数更多，并且在杂交花朵上花费的时间更多。
这些结果表明，近亲繁殖可以（1）改变已知介导传粉者吸引的花部特征；（2）减少花部报酬的产生（在曼陀罗中，花粉是唯一的报酬）；（3）在野外条件下对传粉者的访问产生不利影响。
