Evolutionary Adaptation of Genes Involved in Galactose Derivatives Metabolism in Oil-Tea Specialized Species.

Oil-tea () is a woody oil crop whose nectar includes galactose derivatives that are toxic to honey bees. Interestingly, some mining bees of the genus can entirely live on the nectar (and pollen) of oil-tea and are able to metabolize these galactose derivatives. We present the first next-generation genomes for five and one species that are, respectively, specialized and non-specialized oil-tea pollinators and, combining these with the published genomes of six other species which did not visit oil-tea, we performed molecular evolution analyses on the genes involved in the metabolizing of galactose derivatives. The six genes (, , , , , and ) involved in galactose derivatives metabolism were identified in the five oil-tea specialized species, but only five (with the exception of ) were discovered in the other species. Molecular evolution analyses revealed that , , and in oil-tea specialized species appeared under positive selection. RNASeq analyses showed that , , and were significantly up-regulated in the specialized pollinator compared to the non-specialized pollinator . Our study demonstrated that the genes , , and have played an important role in the evolutionary adaptation of the oil-tea specialized species.