Master of Science
Thompson, Graham J.
Social insects such as the honey bee (Apis mellifera) are well known for their reproductive division of labour and eusocial colony systems. Honey bee workers forgo reproduction in favour of being selfless in directing reproductive benefits towards their queen mother. This altruistic tendency is a result of both behavioural and physiological changes under control of the presence of the queen’s mandibular pheromone. The genetic mechanism that underlies this response is, however, not well understood. Here, this study used RNA interference to knock down the expression of single genes (fruitless and ftz-f1) that have been previously identified as influential in regulating this response to the queen’s pheromone. Cage experiments were performed to monitor changes to worker behaviour, gene expression and physiology. This study could not conclusively confirm that the target genes were indeed knocked down (due to small sample size); however, it was determined that certain ftz-f1 siRNA treatments caused a significant impact on the ovarian development of the worker bees. Future studies would need to confirm that this is due to that fact that the gene was knocked down.
Summary for Lay Audience
Honey bees (Apis mellifera), as other social insects, display a distinct division of labour within their colony. This eusocial system is divided between reproductive (queen and drone) and nonreproductive (worker) castes. These castes coexist within a single colony and for this system to be maintained the workers behave altruistically, directing reproductive benefits towards their queen. Workers completely forgo their own reproduction and behave in such a way to help their queen to be as reproductively successful as possible, including behaviours such as caring for the queen and her larvae, cleaning the hive and collecting food. This has led to an interesting evolutionary problem in the eyes of biologists, how does this behaviour evolve if the workers do not reproduce and cannot pass on their own genes? Interestingly, the workers are maximizing their “inclusive fitness” instead of directing reproducing on their own, they are indirectly passing on their genes through a related individual, their queen mother. The queen helps to facilitate this behaviour by giving off a pheromone that causes repression of workers ovaries leading workers to have underdeveloped ovaries. Certain genes have been identified that are differentially expressed between ovary-active and ovary-inactive workers as well as between bees in the presence of queen pheromone versus its absence. These analyses have led to lists of potential genes, with few being tested functionally, to see if they are responsible for causing ovary inactivation. This research selected two genes, fruitless and fushi tarazu transcription factor 1 (ftz-f1) as they have been identified as potential “hub” genes for worker sterility behaviour. To test function of these genes in workers, a technique called RNA interference was used, which lowers expression of target genes, to test if workers’ ovaries have a different response to queen pheromone in the absence of the products of these genes. Specifically, this involved seeing if the treated workers would have more developed ovaries than the control workers. This research found that certain siRNA treatments for ftz-f1 affected ovary development in workers; however, gene knockdowns did not work for fruitless and there was insufficient data to determine if ftz-f1 was knocked down.
Gallo, Anthony J., "RNA interference of worker sterility genes: Testing mechanisms of reproductive regulation in Apis mellifera" (2019). Electronic Thesis and Dissertation Repository. 6653.