Effects of gene flow on phenotype matching between two varieties of Joshua tree (Yucca brevifolia; Agavaceae) and their pollinators

In animal-pollinated plants, local adaptation to pollinator behaviour or morphology can restrict gene flow among plant populations; but gene flow may also prevent divergent adaptation. Here, we examine possible effects of gene flow on plant-pollinator trait matching in two varieties of Joshua tree (Agavaceae: Yucca brevifolia). The two varieties differ in strikingly in floral morphology, which matches differences in the morphology of their pollinators. However, this co-divergence is not present at a smaller scale: within the two varieties of Joshua tree, variation in floral morphology between demes is not correlated with differences in moth morphology. We use population genetic data for Joshua tree and its pollinators to test the hypotheses that gene flow between Joshua tree populations is structured by pollinator specificity, and that gene flow within the divergent plant-pollinator associations “swamps” fine-scale co-adaptation. Our data show that Joshua tree populations are structured...在动物传粉植物中，对传粉者行为或形态的局部适应（local adaptation）会限制植物种群间的基因流（gene flow）；但基因流同时也可能阻碍分化适应（divergent adaptation）。本研究以约书亚树（龙舌兰科：短叶丝兰，Yucca brevifolia）的两个变种为对象，探讨基因流对植物-传粉者性状匹配的潜在影响。这两个变种的花形态存在显著差异，且与其传粉者的形态差异相匹配。然而，这种共分化（co-divergence）现象在更小的尺度上并不存在：在约书亚树的两个变种内部，居群（deme）间的花形态变异与蛾类传粉者的形态差异并无关联。本研究利用约书亚树及其传粉者的种群遗传数据，检验两个假说：一是约书亚树种群间的基因流由传粉者特异性塑造；二是分化的植物-传粉者互作体系内的基因流会“冲淡”精细尺度的共适应（fine-scale co-adaptation）。本研究数据显示，约书亚树种群的遗传结构