The ant queen's chemical crown
Much like humans, social insects such as ants and bees behave differently when their mother is not around. Workers are thought to perceive the presence of their mother queen using her unique pheromones. New research1 in ants has tracked down the elusive queen pheromone for the first time and revealed that workers are capable of developing ovaries in preparation for laying eggs in absence of pheromones.
The defining feature of social insects is that societies contain queens which specialise in laying eggs, as well as workers, which are mostly infertile but take care of the offspring and the nest. However, when the queen dies or is re-moved, workers begin laying eggs of their own. Previous observations have sug-gested that queens possess a specific pheromone which keeps the workers infer-tile, but the pheromone has never been identified except in the well-studied hon-eybee. Queen pheromones have a lot to tell us about how sociality evolved. For example, if the pheromone was found to be brain-washing the workers into doing something that was bad for them, this would suggest that sociality is rife with hidden conflicts. Alternatively, the pheromone might be more like an advertise-ment that demonstrates to the workers that the queen is doing a good job. Work-ers that can smell that their queen is laying lots of eggs are expected to remain in-fertile and let the queen do what she does best.
After identifying a candidate queen pheromone in the black garden ant2, researchers from the Centre for Social Evolution at the University of Copenhagen (Luke Holman, Charlotte Jørgensen, John Nielsen and Patrizia d'Ettorre) made a synthetic copy of the pheromone to definitively test its function. They found that worker ants separated from their queen developed large ovaries in preparation for laying eggs. However, if the orphaned ants were given a glass model queen coated in synthetic queen pheromone, they remained infertile. The authors also found that the queen's eggs are covered in pheromone, and that sick queens pro-duced less pheromone. Together, these results suggest that the queen phero-mone lets the workers know that the queen is laying many eggs and is in good health.
The queen pheromones of other social insects, including wasps and ter-mites, remain to be found. More will hopefully be discovered soon, and we will be able to determine whether there are universal queen pheromones, or whether they are highly specific to each species. This will reveal how fast the pheromones evolve and shed light on why specific chemicals became queen pheromones.
1. Holman, L., C. G. Jørgensen, J. Nielsen and P. d'Ettorre. 2010. Identi-fication of an ant queen pheromone regulating worker sterility. Pro-ceedings of the Royal Society B. In press.
2. Holman, L., S. Dreier and P. d'Ettorre. 2010. Selfish strategies and honest signalling: reproductive conflicts in ant queen associations. Proceedings of the Royal Society B 277: 2007-2015.
Post Doc Luke Holman, Center for Social Evolution, Department of Biology, University of Copenhagen
Tel. +45 3532 1255