February 12, 2010
Organisms in the wild, particularly those at the base of the food chain, have evolved various ways to communicate about their natural surroundings. Family groups, such as the prairie dog shown to the left, even divvy up chores to the benefit the entire family. One or two siblings keep an eye out for predators, which allows everyone else to spend time eating (for example) and not watching the skies for a hungry hawk. Birds sound alert calls when a predator is in the area. Beavers slap their tails on the water when danger nears.
Insects provide perhaps the most familiar examples of group cooperation. Termites, ants, wasps, and honey bees live in large collectives, or "superorganisms", comprised of thousands, or even tens of thousands, of individuals. A combination of scent and sight signals keep the colonies organized. In honey bees, the queen lays eggs. Nurse bees tend to the eggs and larvae. Worker bees keep the hive clean, make honeycomb and turn nectar into honey. Guard bees prevent intrusions into the hive. Foragers collect pollen and nectar. Drones propegate the genetic lineage of the queen.
A complex set of physical movements and pheromones help coordinate the actions of the 40 or 50 thousand bees in the colony. The way forager bees move when they return to the hive tells nestmates which direction and how far to fly to find pollen or nectar, and how excited the forager was about the quality of the food. The worker bees who come in contact with the queen carry her odure through the hive. This signal assures the workers that all is right with the hive, or may tell them it's time to raise a new queen. All of these signals are seen as "positive feedback" - the signal sent by the individual elicits a positive response: fly to this flower, make a new queen, sting this intruder. Do this, do that.
The opposite, a negative feedback signal, has been documented only once in an insect superorganism. A type of ant was proven to lay a "don't walk this way" odor on paths that led to poor food sources. Dr. James Nieh of the University of California, San Diego has uncovered a second system in honey bees, one that warns foragers that a food source is dangerous. "It is perhaps the most sophisticated because it counters the positive feedback of the waggle dance," Nieh writes.
Praying Mantis dining on a bee
Photo by Sally King, National Park Service
Bandilier National Monument
Through a series of tests, Nieh's research team looked at honey bees who went to a food source (in this case a feeder) and encountered simulated predators that grabbed them, or the smell of a bee alarm pheromone. Once these near-victims returned to the hive, they approached other bee foragers that smelled like that same food source. If the other foragers started doing the "there's food here!" dance, the near-victims vibrated at a specific frequency while touching the foraging bees. The foraging bees tended to stop dancing - and therefore stop telling other bees in the hive where to find that particular source of food.
On the surface, this seems like the honey bee's equivalent to the prairie dog's "chuck-chuck-chuck!", which sends its brethren scurrying for cover. But as Nieh explains, danger signals in other animals tend to elicit a fight-or-flight response. They either hide or attack the intruder. The unique thing about the honey bee stop signal is that it responds to the food dancer - a fellow honey bee - and not the danger directly. A very small in-hive argument if you will. "Go here for food!" says the forager. "No, don't go here, there's danger!", warns the stop signaler.
"The stop signal," writes Nieh, "is very specifically countering the honey bee dance language by telling [food] dancers that they should cease recruiting nestmates to a dangerous location."
For more information:
- A Negative Feedback Signal That Is Triggered by Peril Curbs Honey Bee Recruitment (Current Biology, 11 February 2010 Online edition)
- Watch the video at the UCSD News Room
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