The Epigenetics Revolution

In the formation of a new colony, a virgin queen leaves a hive, accompanied by a swarm of workers. She’ll mate with some males and then settle down to form a new colony. The queen will lay thousands of eggs, most of which will hatch and develop into more workers. A few eggs will hatch and develop into new queens, who can start the whole cycle all over again.

Because the queen who founded the colony mated several times, not all the bees in the colony will be genetically identical to each other, because some of them will have different fathers. But there will be groups of thousands and thousands of genetically identical bees in any colony. This genetic identity doesn’t refer only to the worker bees. The new queens are genetically identical to thousands of worker bees in the colony. We could call them sisters, but this doesn’t really describe them well enough. They are all clones.

However, a new queen and her clonal worker sisters are clearly incredibly different from each other, both in physical form and in activities. The queen can be twice the size of a worker bee. After the so-called nuptial flight, when she first leaves a colony and mates, the queen almost never leaves the hive again. She stays in the darkness of the interior, laying up to 2,000 eggs a day in the summer months. She has no sting barbs, no wax glands and no pollen baskets (not much point having a shopping bag if you never leave the house). Worker bees have a lifespan that can usually be measured in weeks, whereas queens live for years[262].

Conversely, workers can do many things that the queens can’t. Chief amongst these is collecting food, and then telling the rest of the colony its location. This information is communicated using the famous ‘waggle dance’. The queen lives in darkened luxury, but she never gets to boogie.

So, a honeybee colony contains thousands of individuals who are genetically identical, but a few of them are really different physically and behaviourally. This difference in outcome is all down to how the bee larvae are fed. The pattern of early feeding completely determines whether a larva will develop into a worker or into a queen.

For honeybees the DNA script is constant but the outcome is variable. The outcome is controlled by an early event (feeding pattern) which sets a phenotype that is maintained throughout the rest of life. This is a scenario that just shrieks epigenetics at us, and in the last few years scientists have started to unravel the molecular events that underpin this process.

The critical roll of the dice for honeybees happens after the third day of life, as a fairly immobile grub or larva. Until day three, all honeybee larvae are given the same food. This is a substance called royal jelly, which is produced by a specialised group of workers. These young workers are known as nurse bees and they secrete royal jelly from glands in their heads. Royal jelly is a highly nutritious food source. It is a concentrated mix of a lot of different components, including key amino acids, unusual fats, specific proteins, vitamins and other nutrients that haven’t been well-characterised yet.

Once the larvae are three days old, the nurse bees stop feeding royal jelly to most of them. Instead, most larvae are switched onto a diet of pollen and nectar. These are the larvae which will grow up to be worker bees.

But for reasons that nobody really understands, the nurse bees continue feeding royal jelly to a select few larvae. We don’t know how these larvae are chosen or why. Genetically they are identical to the ones that are switched onto the less sophisticated diet. But this small group of larvae that continue to be nourished with royal jelly grow up to be queens, and they’re fed this same substance throughout their lives. The royal jelly is essential for the production of mature ovaries in the queens. Worker females never develop proper ovaries, which is one of the reasons they are infertile. Royal jelly also prevents the queen from developing the organs that she won’t ever need, like those pollen baskets.

We understand some of the mechanisms behind this process. Bee larvae contain an organ that has some of the same functions as our liver. When a larva receives royal jelly continuously, this organ processes the complex food source and activates the insulin pathway. This is very similar to the hormonal pathway in mammals that controls the levels of sugar in the bloodstream. In honeybees activation of this pathway increases production of another hormone, called Juvenile Hormone. Juvenile Hormone in turn activates other pathways. Some of these stimulate growth and development of tissues like the maturing ovaries. Others shut down production of the organs that the queen doesn’t need[263].

Mimicking royalty