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

Abstract

Diet specialization may affect the population genetic structure of pollinators by reducing gene flow and driving genetic differentiation, especially in pollen‐specialist bees. Colletes gigas is a pollen‐specialist pollinator of Camellia oleifera , one of the most important staple oil crops in China. Ca . oleifera blooms in cold climates and contains special compounds that make it an unusable pollen source to other pollinators. Thus, C . gigas undoubtedly plays a key role as the main pollinator of Ca . oleifera , 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 C . gigas . 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 ( R = .866, p = .008) and linear regression ( R 2 = .616, p < .001). Precipitation and sunshine duration were positively and significantly ( R ≥ .765, p ≤ .016) correlated with observed heterozygosity ( H o ) and expected heterozygosity ( H e ). These results showed that C . gigas 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 C . gigas 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 C . gigas 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.

Genomic Patterns of Iberian Wild Bees Reveal Levels of Diversity, Differentiation and Population Structure, Supporting the “Refugia within Refugia” Hypothesis

“…Several studies that compared genetic diversity between oligolectic vs. polylectic species have found that the former show lower genetic diversity [26,28,60] and higher differentiation [27,60]. It has been hypothesized that such a decrease in genetic diversity may be caused by a lower effective population size and greater population isolation, caused by lower abundance of host plants [26,28,60,61]. However, this hypothesis lacks empirical validation, and in Mediterranean areas, certain plant species or botanical families used by oligolectic species can be hyper-abundant, such as Brassicaceae, the sole pollen source for A. agilissima.…”

The impact of geography and climate on the population structure and local adaptation in a wild bee

“…Following angiosperms that were able to occupy new suitable habitats as the ice gradually retreated (Hewitt, 1996 ), insect populations started a similar recolonization process (Shell & Rehan, 2016 ). The postglaciation refugia hypothesis has been examined on other continents: for example, a pollen‐specialist bee Colletes gigas endemic to China was shown to exhibit fluctuations in effective population size during the last glacial maximum (Su et al, 2022 ).…”

The mechanism of Andrena camellia in digesting toxic sugars

“… 11 Thus, C. oleifera depends heavily on the wild pollinator Andrena camellia . 12 , 13 In the last two decades, A. camellia has declined sharply due to crop monoculture in C. oleifera forests, habitat destruction of A. camellia , intensification of anthropogenic activities, and abuse of pesticides (insecticides and herbicides). 11 A. camellia nests are declining dramatically.…”