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Surprise in bee reproduction

By Dave Armstrong - 25 Sep 2013 4:17:13 GMT
Surprise in bee reproduction

Look out, there's a queen about! Bumblebees image; Credit: © Shutterstock

How can an individual beat the system? Humans are quite good at it, and I suspect some dolphins are adept, but in the set style of insect social systems, is there any sign of respite from the daily grind, outside of cartoons?

The humble bumblebee, Bombus terrestris, is seen here to be very flexible in its productive possibilities. With queen dominance highly developed in colonies, one hope for an alternative is recruitment of worker females. Pierre Blacher and his colleagues from Sorbonne Paris Cite´ and Universidade de Sao Paulo (USP) have discovered a drifting of fertile female workers near the end of a colony's life. They move to neighbouring colonies (as well as being capable of producing some eggs in their own colony) and find this strategy successful.

Now this is not the way it's supposed to work! The queen rules, as in chess, and although in other species, she is simply an egg-laying machine, the bumblebee queen is big and business-like in founding colonies, rearing workers and ruling her roost.

In experiments, the monitoring of workers' inter-colony movement led to the idea of a dynamic set of behaviours by both infertile and fertile females. Competition between those capable of reproducing within a nest is probably much greater than was previously thought. The ordinary bee can be similar to the single mated queen in these experimental colonies.

While non-drifting workers had no oocyte (egg) development, ovary activation could follow either isolation or "drifting." Just over half of all workers visited at least one foreign nest in these experiments, which is many more than has been found before. There was also no aggression between bees from different colonies. This definitely helps to explain the amount of drifting. Neither did the drifters die off more often than other bees.

Egg-laying by drifters was limited to about a third of the fertile bees. The writers presume that these specimens had pre-developed ovaries, although after 6 days in a foreign colony, many workers had low levels of ovarian change. Many of these (78.9%) foraged for their hosts and returned loaded with pollen. Why these infertile workers would do this is difficult to explain. In the same way, an explanation of how drifting first came about would help to explain the evolutionary position. These bumblebees do give clues about how potentially the drifting could have affected the appearance of many social bee and other social insect systems.

It is the previously-unknown flexibility of this humble species that impresses most. They can reproduce in their own nest when the queen is less competitive, after the early development of the colony. Then they can reproduce in other colonies. Gynes are the future queens grown later in the colony. Their appearance causes this switch in workers' behaviour. Their presence seems to release the fertile workers from their responsibilities. They can produce male bees for mating , as they are unfertilised themselves. (Haploid eggs are all male in bees, with the fertilised diploids becoming the female worker or queen.) The worker would have to be dominant in its own nest to produce eggs, but, in foreign nests, with this lack of aggression shown, it would be easier to lay eggs.

These colonies are smaller than the large social insect colonies of wasps or honey bees, leading to recruitment of these workers being quite useful for the species as a whole. The evolutionary step they have made in allowing "drifting" is really significant for our understanding of the social insect.

The researchers wrote the paper in the Proceedings of the Royal Society:B.