Effects of environmental contaminants on gene expression, DNA methylation and gut microbiota in Buff-tailed Bumble bee - Bombus terrestris

Bee populations are increasingly at risk. In this thesis, I explore various mechanisms through which environmental contaminants, namely imidacloprid and black carbon, can affect bumble bee epigenetics, behaviour and gutmicrobiota. I found imidacloprid has numerous epigenetic effects on Bombus terrestris non reproductive workers. I analysed three whole methylome (BS-seq) libraries and seven RNA-seq libraries of the brains of imidacloprid exposed workers and three BS-seq libraries and nine RNA-seq libraries fromunexposed, control workers. I found 79, 86 and 16 genes differentially methylated at CpGs, CHHs and CHGs sites respectively between groups. I found CpG methylation much more focused in exon regions compared with methylation at CHH or CHG sites. I found 378 genes that were differentially expressed between imidacloprid treated and control bees. In addition, I found 25 genes differentially alternatively spliced between control and imidacloprid samples. I used Drosophila melanogaster as a model for the behavioural effects of imidacloprid on insects. Imidacloprid did not affect flies’ periodicity. Low doses (2.5 ppb) of imidacloprid increased flies’ activity while high doses (20 ppb) decreased activity. Canton-S strain was more sensitive to imidacloprid during geotaxis assay thanM1217. I proposed that a possible modulator of imidacloprid’s effects on insects is its effects on insects’ gut microbiota. I produced and analysed thirty libraries of 16S rRNA metagenomic data from bee guts dividing by control and imidacloprid. There were no differences in alpha and beta bacterial diversity between groups while the ratio of one species of latobacillus increased in bees exposed to imidacloprid. As an extension of this microbiota work, I researched the effect of black carbon on gut microbiota in the bumble bee. Bacterial cultivation methods showed significant increases of species (CFU) in bees exposed to black carbon and this was also detected by a qPCR approach. However, in a metagenomic analysis, I did not find significant differences in alpha and beta diversity richness between black carbon and control groups.