Miller Chelsea N, Whitehead Susan R, Kwit Charles
Department of Ecology and Evolutionary Biology University of Tennessee Knoxville TN USA.
Department of Biological Sciences Virginia Tech University Blacksburg VA USA.
Ecol Evol. 2020 Feb 27;10(6):2860-2873. doi: 10.1002/ece3.6101. eCollection 2020 Mar.
Morphological and chemical attributes of diaspores in myrmecochorous plants have been shown to affect seed dispersal by ants, but the relative importance of these attributes in determining seed attractiveness and dispersal success is poorly understood. We explored whether differences in diaspore morphology, elaiosome fatty acids, or elaiosome phytochemical profiles explain the differential attractiveness of five species in the genus to eastern North American forest ants. Species were ranked from least to most attractive based on empirically-derived seed dispersal probabilities in our study system, and we compared diaspore traits to test our hypotheses that more attractive species will have larger diaspores, greater concentrations of elaiosome fatty acids, and distinct elaiosome phytochemistry compared to the less attractive species. Diaspore length, width, mass, and elaiosome length were significantly greater in the more attractive species. Using gas chromatography-mass spectrometry, we found significantly higher concentrations of oleic, linoleic, hexadecenoic, stearic, palmitoleic, and total fatty acids in elaiosomes of the more attractive species. Multivariate assessments revealed that elaiosome phytochemical profiles, identified through liquid chromatography-mass spectrometry, were more homogeneous for the more attractive species. Random forest classification models (RFCM) identified several elaiosome phytochemicals that differed significantly among species. Random forest regression models revealed that some of the compounds identified by RFCM, including methylhistidine (-amino acid) and d-glucarate (carbohydrate), were positively related to seed dispersal probabilities, while others, including salicylate (salicylic acid) and citrulline (amino acid), were negatively related. These results supported our hypotheses that the more attractive species of -which are geographically widespread compared to their less attractive, endemic congeners-are characterized by larger diaspores, greater concentrations of fatty acids, and distinct elaiosome phytochemistry. Further advances in our understanding of seed dispersal effectiveness in myrmecochorous systems will benefit from a portrayal of dispersal unit chemical and physical traits, and their combined responses to selection pressures.
蚁播植物中传播体的形态和化学属性已被证明会影响蚂蚁对种子的传播，但这些属性在决定种子吸引力和传播成功率方面的相对重要性却鲜为人知。我们探究了传播体形态、油质体脂肪酸或油质体植物化学特征的差异是否能解释该属五种植物对北美东部森林蚂蚁的不同吸引力。在我们的研究系统中，根据经验得出的种子传播概率，将这些物种从吸引力最小到最大进行排序，我们比较了传播体特征，以检验我们的假设：与吸引力较小的物种相比，吸引力较大的物种将具有更大的传播体、更高浓度的油质体脂肪酸以及独特的油质体植物化学特征。在吸引力较大的物种中，传播体的长度、宽度、质量和油质体长度显著更大。通过气相色谱 - 质谱联用，我们发现吸引力较大的物种的油质体中油酸、亚油酸、十六碳烯酸、硬脂酸、棕榈油酸和总脂肪酸的浓度显著更高。多变量评估显示，通过液相色谱 - 质谱联用鉴定出的油质体植物化学特征，在吸引力较大的物种中更为均匀。随机森林分类模型（RFCM）识别出了几种在物种间有显著差异的油质体植物化学物质。随机森林回归模型显示，RFCM鉴定出的一些化合物，包括甲基组氨酸（一种氨基酸）和d - 葡萄糖醛酸（一种碳水化合物），与种子传播概率呈正相关，而其他一些化合物，包括水杨酸盐（水杨酸）和瓜氨酸（一种氨基酸），则呈负相关。这些结果支持了我们的假设：与吸引力较小的同属特有物种相比，在地理上分布广泛的吸引力较大的物种具有更大的传播体、更高浓度的脂肪酸以及独特的油质体植物化学特征。对蚁播系统中种子传播有效性的进一步理解将受益于对传播单元化学和物理特征及其对选择压力的综合响应的描述。
