Population genomics and phylogeography of , a wild bee specialized on winter flowering plants.

Diet specialization may affect the population genetic structure of pollinators by reducing gene flow and driving genetic differentiation, especially in pollen-specialist bees. is a pollen-specialist pollinator of , one of the most important staple oil crops in China. . blooms in cold climates and contains special compounds that make it an unusable pollen source to other pollinators. Thus, . undoubtedly plays a key role as the main pollinator of . , with biological and economic significance. Here, we use a population genomic approach to analyze the roles of geography and climate on the genetic structure, genetic diversity, and demographic history of . . A total of 1,035,407 SNPs were identified from a 582.77 Gb dataset. Clustering and phylogenetic analyses revealed a marked genetic structure, with individuals grouped into nine local clusters. A significant isolation by distance was detected by both the Mantel test ( = .866, = .008) and linear regression ( = .616, < .001). Precipitation and sunshine duration were positively and significantly ( ≥ .765, ≤ .016) correlated with observed heterozygosity ( ) and expected heterozygosity ( ). These results showed that . populations had a distinct phylogeographic pattern determined by geographical distance and environmental factors (precipitation and sunshine duration). In addition, an analysis of paleogeographic dynamics indicated that . populations exhibited patterns of glacial expansion and interglacial contraction, likely resulting from post-glacial habitat contraction and fragmentation. Our results indicated that the peculiar phylogeographic patterns in . populations may be related to their specialization under long-term adaptation to host plants. This work improves our understanding of the population genetics in pollen-specialist bees. The distinct genetic clusters identified in this study should be taken into consideration for the protection and utilization of this specialized crop pollinator.