Abstract
The reproductive division of labor, based on caste differentiation in social insects, is of great significance in evolution. Generally, a healthy bee colony consists of a queen and numerous workers and drones. Despite being genetically identical, the queen and workers exhibit striking differences in morphology, behavior, and lifespan. The fertilized eggs and larvae selectively develop into queen and worker bees depending on the local nutrition and environment. Bee worker larvae that are transplanted within 3 days of age to queen cells of a bee colony can develop into queens with mature ovaries. This phenomenon is important to understand the regulatory mechanisms of caste differentiation. In this study, we transplanted worker larvae (Apis mellifera) at the age of 1 (L1), 2 (L2), and 3 days (L3) into queen cells until the age of 4 days. Subsequently, genetic changes in these larvae were evaluated. The results revealed that the number of differentially expressed genes (DEGs) in L1 vs. L3 was more than that in L1 vs. L2. Furthermore, many of the genes that were downregulated are mostly involved in metabolism, body development, reproductive ability, and longevity, indicating that these functions decreased with the age of transplantation of the larvae. Moreover, these functions may be critical for worker larvae to undergo the developmental path to become queens. We also found that the DEGs of L1 vs. L2 and L1 vs. L3 were enriched in the MAPK, FoxO, mTOR, Wnt, TGF-beta Hedgehog Toll and Imd, and Hippo signaling pathways. Gene ontology analysis indicated that some genes are simultaneously involved in different biological pathways; through these genes, the pathways formed a mutual regulatory network. Casein kinase 1 (CK 1) was predicted to participate in the FoxO, Wnt, Hedgehog, and Hippo signaling pathways. The results suggest that these pathways cross talked through the network to modify the development of larvae and that CK 1 is an important liaison. The results provide valuable information regarding the regulatory mechanism of environmental factors affecting queen development, thus, amplifying the understanding of caste differentiation in bees.
Highlights
The efficient and refined division of labor among social insects, such as termites, wasps, ants, and bees, plays a key role in their ecological success (Wilson, 1985)
Complementary DNA libraries were constructed from mRNA that was isolated using the TruSeq Stranded Total RNA Sample Prep Kit, based on enrichment with oligo magnetic beads and fragmentation in fragmentation buffer
After filtering the adaptor sequences, over 86.36 million clean reads were produced in each library
Summary
The efficient and refined division of labor among social insects, such as termites, wasps, ants, and bees, plays a key role in their ecological success (Wilson, 1985). Marked differences exist between the queen and worker bees in terms of morphology, behavior, reproductive ability, function, and life span (Wilson, 1971) This phenomenon in social insects is known as caste determination and is affected by environmental factors (West-Eberhard, 1989; Evans and Wheeler, 2001). Both the queen and worker bees develop from fertilized eggs, the larvae gradually develop to a queen and worker bees, depending on the environment (Cristino et al, 2006). The differential regulation of development led to caste determination, eventually leading to reproductive division of labor; our study provides valuable information on the regulatory mechanisms of environmental factors affecting the quality of a queen and amplifying the understanding of caste differentiation in bees
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