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.