Data from: 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 by pollinator association, but the two tree varieties are only weakly isolated—meaning that their phenotypic differences are maintained in the face of significant gene flow. Coalescent analysis of gene flow between the two Joshua tree types suggests that it may be shaped by asymmetric pollinator specificity, which has been observed in a narrow zone of sympatry. Finally, we find evidence suggesting that gene flow among Joshua tree sites may shape floral morphology within one plant-pollinator association, but not the other.

在动物传粉植物中，对传粉者行为或形态的局部适应（local adaptation）可限制植物种群间的基因流（gene flow）；而基因流也可能阻碍种群间的趋异适应（divergent adaptation）。本研究以两种变种的约书亚树（Agavaceae：*Yucca brevifolia*）为研究对象，探讨基因流对植物-传粉者性状匹配（trait matching）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，这种共趋异（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，不同居群（deme）间的花形态变异与蛾类传粉者的形态差异并无关联。我们利用约书亚树及其传粉者的种群遗传数据（population genetic data），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（pollinator specificity）塑造；二是趋异的植物-传粉者共生关系内的基因流会“淹没”精细尺度的共适应（co-adaptation）。研究数据显示，约书亚树种群的遗传结构由传粉者关联所塑造，但两个树变种间的遗传隔离程度极低——这意味着尽管存在显著的基因流，二者的表型差异仍得以维持。对两种约书亚树类群间基因流的溯祖分析（coalescent analysis）表明，其基因流可能受不对称传粉者特异性（asymmetric pollinator specificity）调控，这一现象已在狭窄的同域分布区（sympatry）中被观测到。最后，我们发现证据表明，约书亚树各样地间的基因流可能会影响其中一种植物-传粉者共生关系内的花形态，但对另一种则无此作用。