Many compounding factors have been implicated in the global decline of native bees, including but not limited to land use changes, inbreeding, and pathogens. Bumble bees (Bombus sp) are one of the first insect groups where lab-reared individuals with lower genetic diversity have been documented to have a weakened immune response and overall higher infection susceptibility. This is particularly interesting given that recent land-use changes have been identified as features significantly limiting gene flow in wild Bombus. Despite this fact, few studies have examined bee host and pathogen population genetics across landscape scales. Given increasing urbanization and agricultural expansion, it is critical to understand how changing landscapes affect both the genetic connectivity of bees and infectious disease dynamics such as transmission.
In this study, we investigate the landscape genetic structure of B. vosnesenkii across a 1000km study region of the southwestern US coast. A total of 10 microsatellites in B. vosnesenkii were sequenced to measure heterozygosity and allelic richness. FST, F’ST, and Dest were calculated in each population structure was estimated using STRUCTURE v.2.3.4. Additionally, multi-plex PCR was used to determine the prevalence of three parasite classes: microsporidians, neogregarines, and trypanosomes.
Results/Conclusions
vosnesenksii populations show significant differentiation across all statistics; FST = 0.041, F’ST = 0.044, and Dest = 0.155. Three distinct biogeographic areas, Coastal, Sierra, and Island were sampled, though these did not show strong genetic structuring, likely due to long distance dispersal. However, the island populations show small but significant inbreeding, which may yet prove relevant for parasite persistence and virulence.
Infection prevalence showed a latitudinal gradient north to south, and was highly variable both across the study region and within biogeographic regions. Trypanosomes, most commonly represented by Crithidia bombi, showed upwards of 35% infection prevalence at certain sites. Variation in infection prevalence among colony members was also substantial, opening new questions concerning intra-colony transmission. Future research will expand on genetic and landscape-level drivers of co-infection and strain diversity.