Female Developmental Environment Delays Development of Male Honeybee (Apis Mellifera)

Abstract

Background Nutrition and cell size play an important role in the determination of caste differentiation in queen-worker of honeybee (Apis mellifera), whereas the haploid genome dominates the differentiation of drones. However, the effects of female developmental environment on the development of males remain unclear. In this study, young drone larvae were transferred into worker cells (WCs) or remained in drone cells (DCs) to rear drones. The parts of drone larvae were also grafted into queen cells (QCs) for 48 h and then transplanted into drone cells until emerging. Morphological indexes and reproductive organs of these three types of newly emerged drones were measured. Newly emerged drones and 3 d drone larvae from WCs, DCs and QCs were sequenced by RNA sequencing (RNA-Seq). Results Morphological results showed that newly emerged DC drones had bigger body sizes and more well-developed reproductive tissues than WC and QC drones, whereas the reproductive tissues of QC drones were relatively better than those of WC drones. Gene expression results showed a more clear difference among three groups. At the larval stage, there were 889, 1761 and 1927 significantly differentially expressed genes (DEGs) in WC/DC, QC/DC and WC/QC comparisons, respectively. The number of DEGs decreased in adult drones of these three comparisons [678 (WC/DC), 338 (QC/DC) and 518 (WC/QC)]. A high number of DEGs were involved in sex regulation, growth, olfaction, vision, mammalian target of rapamycin (mTOR), Wnt signaling pathways, etc. Weighted gene co-expression network analysis (WCGNA) showed that WC and DC larvae were closer than QC larvae, whereas QC and WC drones were closer than DC drones. These results revealed that DC drones had better development in the body and reproductive system than QC and WC drones. Conclusion This study demonstrated that the developmental environment of honeybee females including the larval diet and cell size delayed male development. Naturally, honeybee colony ovigerous workers in queen-less colonies or non-mated queens produce a large number of dysplasia drones which are not well-developed. Therefore, this study serves as a model for understanding the regulation of sexual differentiation in social insects by environmental factors.