Genetic Variability of the Neogregarine Apicystis bombi, an Etiological Agent of an Emergent Bumblebee Disease

Abstract

The worldwide spread of diseases is considered a major threat to biodiversity and a possible driver of the decline ofpollinator populations, particularly when novel species or strains of parasites emerge. Previous studies have suggested thatpopulations of introduced European honeybee (Apis mellifera) and bumblebee species (Bombus terrestris and Bombusruderatus) in Argentina share the neogregarine parasite Apicystis bombi with the native bumblebee (Bombus dahlbomii). Inthis study we investigated whether A. bombi is acting as an emergent parasite in the non-native populations. Specifically,we asked whether A. bombi, recently identified in Argentina, was introduced by European, non-native bees. Using ITS1 andITS2 to assess the parasite?s intraspecific genetic variation in bees from Argentina and Europe, we found a largelyunstructured parasite population, with only 15% of the genetic variation being explained by geographic location. The mostabundant haplotype in Argentina (found in all 9 specimens of non-native species) was identical to the most abundanthaplotype in Europe (found in 6 out of 8 specimens). Similarly, there was no evidence of structuring by host species, withthis factor explaining only 17% of the genetic variation. Interestingly, parasites in native Bombus ephippiatus from Mexicowere genetically distant from the Argentine and European samples, suggesting that sufficient variability does exist in the ITSregion to identify continent-level genetic structure in the parasite. Thus, the data suggest that A. bombi from Argentina andEurope share a common, relatively recent origin. Although our data did not provide information on the direction of transfer,the absence of genetic structure across space and host species suggests that A. bombi may be acting as an emergentinfectious disease across bee taxa and continents.