The Role of Nutrition as an Epigenetic Modulator of Phenotypic Plasticity during Honeybee Development

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Honeybees are insect pollinators that are responsible for around 10% of the value of world food production. They live in complex societies comprising tens of thousands of individuals, most of these are female worker honeybees that are unable to reproduce and instead devote their short lives to finding food in flowers (nectar/pollen) and other tasks such as nursing larvae. In addition to these sterile female bees, the hive also contains male drones and a single female bee called the queen that has a much longer life span and can reproduce. The queen can lay fertilised or unfertilised eggs. Unfertilised eggs are fed drone jelly followed by nectar/pollen and become male drones, while fertilised eggs can become either queen or worker bees. Whether a fertilised egg results in a larva that will become an adult worker or queen bee depends on the type of food the larva is fed. Larvae destined to become workers are fed worker jelly followed by a diet of nectar/pollen and those destined to become queens are fed royal jelly. These differing diets are then maintained over the entire lifetime of the adult. The ability of an individual honeybee larva to become a queen, worker or drone cannot be because of different DNA: the genome of that larva has the capacity to become all three, it is due to the way genes are switched on or off in response to the specific diet; this determines such differing developmental outcomes. Epigenetics is a dynamic set of instructions that exist 'on top' of the genetic information, that can encode and direct multiple different outcomes from a fixed DNA sequence. There are two main families of epigenetic mechanisms; one type marks the actual DNA sequence, the other type marks proteins called histones that the DNA tightly wraps itself around in order to fit into the nucleus of a cell. These small chemical tags, or epigenetic/histone modifications, allow histones to act differently depending on which tags they have, usually by allowing access to the DNA and genes. Importantly, this enables identical DNA sequences to behave in different ways and provides the needed flexibility to coordinate the expression of all genes and respond to changing environmental factors.We previously hypothesised that the differing diets of queens and workers could determine alternative developmental outcomes via these histone proteins. Through previous BBSRC funding, we demonstrated for the first time that queens and workers have their own specific epigenetic histone patterns even though their DNAs are the same, and that these differences correlate with queen and worker -specific gene expression. Unexpectedly, we also found that some of the most important epigenetic differences were in regions of the honeybee genome that are not part of genes and that these non-coding regions of DNA may be crucial in making a queen or a worker. In order to determine if it is these regions that are sensitive to diet, we will first characterise them and confirm they are the main determinants/regulators of queen, worker and drone development. We will determine exactly how they function by following their changing epigenetic patterns through the early stages of honeybee development and identify where the important differences are across the entire genome. We will also look at how these regions interact with genes in the honeybee genome through 3D conformation. Then, we will be able to determine whether an important component of the queen diet can directly change the function of these regions. We will do this by growing individual bee larvae in the laboratory, manipulating their diets and monitoring the effects on their development at the molecular level and at the level of the adult bee, where we can look for queen or worker morphological structures. These experiments will produce the first comprehensive analyses of the three honeybee developmental pathways and also provide the basis for understanding how they are shaped by nutrition.