Stingless bees are generalist pollinators distributed through the pantropical region. There is growing evidence that their wild populations are experiencing substantial decline in response to habitat degradation and pesticides. Policies for conservation of endangered species will benefit from studies focusing on genetic and molecular aspects of their development and behavior. The most common method for looking at gene expression is real-time quantitative polymerase chain reaction preceded by reverse transcription (RT-qPCR) of the mRNA of interest. This method requires the identification of reliable reference genes to correctly estimate fluctuations in transcript levels. To contribute to molecular studies on stingless bees, we used Frieseomelitta varia, Melipona quadrifasciata, and Scaptotrigona bipunctata species to test the expression stability of eight reference genes (act, ef1-α, gapdh, rpl32, rps5, rps18, tbp, and tbp-af) in RT-qPCR procedures in five physiological and experimental conditions (development, sex, tissues, bacteria injection, and pesticide exposure). In general, the rpl32, rps5 and rps18 ribosomal protein genes and tpb-af gene showed the highest stability, thus being identified as suitable reference genes for the three stingless bee species and defined conditions. Our results also emphasized the need to evaluate the stability of candidate genes for any designed experimental condition and stingless bee species.

Background Most of our understanding on the social behavior and genomics of bees and other social insects is centered on the Western honey bee, Apis mellifera. The genus Apis, however, is a highly derived branch comprising less than a dozen species, four of which genomically characterized. In contrast, for the equally highly eusocial, yet taxonomically and biologically more diverse Meliponini, a full genome sequence was so far available for a single Melipona species only. We present here the genome sequence of Frieseomelitta varia, a stingless bee that has, as a peculiarity, a completely sterile worker caste. Results The assembly of 243,974,526 high quality Illumina reads resulted in a predicted assembled genome size of 275 Mb composed of 2173 scaffolds. A BUSCO analysis for the 10,526 predicted genes showed that these represent 96.6% of the expected hymenopteran orthologs. We also predicted 169,371 repetitive genomic components, 2083 putative transposable elements, and 1946 genes for non-coding RNAs, largely long non-coding RNAs. The mitochondrial genome comprises 15,144 bp, encoding 13 proteins, 22 tRNAs and 2 rRNAs. We observed considerable rearrangement in the mitochondrial gene order compared to other bees. For an in-depth analysis of genes related to social biology, we manually checked the annotations for 533 automatically predicted gene models, including 127 genes related to reproductive processes, 104 to development, and 174 immunity-related genes. We also performed specific searches for genes containing transcription factor domains and genes related to neurogenesis and chemosensory communication. Conclusions The total genome size for F. varia is similar to the sequenced genomes of other bees. Using specific prediction methods, we identified a large number of repetitive genome components and long non-coding RNAs, which could provide the molecular basis for gene regulatory plasticity, including worker reproduction. The remarkable reshuffling in gene order in the mitochondrial genome suggests that stingless bees may be a hotspot for mtDNA evolution. Hence, while being just the second stingless bee genome sequenced, we expect that subsequent targeting of a selected set of species from this diverse clade of highly eusocial bees will reveal relevant evolutionary signals and trends related to eusociality in these important pollinators.

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