Towards a molecular definition of worker sterility: differential gene expression and reproductive plasticity in honey bees

We show that differences in the reproductive development of honey bee workers are associated with locus-specific changes to abundance of messenger RNA. Using a cross-fostering field experiment to control for differences related to age and environment, we compared the gene expression profiles of functionally sterile workers (wild-type) and those from a mutant strain in which workers are reproductively active (anarchist). Among the set of three genes that are significantly differentially expressed are two major royal jelly proteins that are up-regulated in wild-type heads. This discovery is consistent with sterile workers synthesizing royal jelly as food for developing brood. Likewise, the relative underexpression of these two royal jellies in anarchist workers is consistent with these workers’ characteristic avoidance of alloparental behaviour, in favour of selfish egg-laying. Overall, there is a trend for the most differentially expressed genes to be up-regulated in wild-type workers. This pattern suggests that functional sterility in honey bee workers may generally involve the expression of a suite of genes that effectively ‘switch’ ovaries off, and that selfish reproduction in honey bee workers, though rare, is the default developmental pathway that results when ovary activation is not suppressed

Effects of carbon dioxide narcosis on ovary activation and gene expression in worker honeybees, Apis mellifera

In an effort to uncover genes associated with ovary activation in honey bee workers, the extent to which eight candidate genes covaried in their expression with experimentally-induced changes in worker reproductive state was examined. Groups of caged, queenless workers narcotized with CO2 on consecutive days early in adult life showed a significantly lower level of ovary activation than did groups of untreated workers. This same experimental treatment, by contrast, is known to accelerate ovary activation and induce egg laying in virgin honey bee queens - an observation that suggests that CO2 narcosis has contrasting effects in queen versus worker ovary activation. Experimentally-induced changes to worker reproductive state were associated with changes in gene expression. Vitellogenin, an egg yolk precursor, and transferrin, an iron transporter, were two transcripts found to be significantly down-regulated as a function of the ovary-inhibiting treatment. CO2 narcosis did not effect the expression of six other genes selected as putative markers for processes that may underlie ovary activation. The results show that the expression of vitellogenin and transferrin is correlated with ovary activation in workers, and may therefore be part of the gene network involved in the regulatory control of functional sterility in honeybees

The transcriptomic changes associated with the development of social parasitism in the honeybee Apis mellifera capensis

Supplementary material: Online Resource 1 (XLSX 15 kb) Online Resource 2 (XLSX 13 kb) Online Resource 3 (PDF 268 kb) Online Resource 4 (XLSX 14 kb) Online Resource 5 (XLSX 29 kb)Social insects are characterized by the division of labor. Queens usually dominate reproduction, whereas workers fulfill non-reproductive age-dependent tasks to maintain the colony. Although workers are typically sterile, they can activate their ovaries to produce their own offspring. In the extreme, worker reproduction can turn into social parasitism as in Apis mellifera capensis. These intraspecific parasites occupy a host colony, kill the resident queen, and take over the reproductive monopoly. Because they exhibit a queenlike behavior and are also treated like queens by the fellow workers, they are so-called pseudoqueens. Here, we compare the development of parasitic pseudoqueens and social workers at different time points using fat body transcriptome data. Two complementary analysis methods—a principal component analysis and a time course analysis—led to the identification of a core set of genes involved in the transition from a social worker into a highly fecund parasitic pseudoqueen. Comparing our results on pseudoqueens with gene expression data of honeybee queens revealed many similarities. In addition, there was a set of specific transcriptomic changes in the parasitic pseudoqueens that differed from both, queens and social workers, which may be typical for the development of the social parasitism in A. m. capensis.The Deutsche Forschungsgemeinschaft (RFAM).http://link.springer.com/journal/1142019-04-01hj2018Zoology and Entomolog