By Joseph Milton
We all struggle to communicate after a sleepless night, let alone pull off our best dance moves, and it seems that honeybees are no different.
Sleep-deprived bees are less proficient than their well-rested hive mates at indicating the location of a food source to other members of the colony by waggle dancing -- the figure-of-eight dance used to communicate the quality and location of nectar supplies to the hive -- according to a study published online this week in the Proceedings of the National Academy of Sciences1.
Like all animals, European honeybees (Apis mellifera) rely on a sleep-like state of inactivity to survive -- but sleep in insects and the effects of sleep deprivation on their behaviour are poorly understood.
Barrett Klein, who led the study as a graduate student at the University of Texas at Austin, says that sleep deprivation could conceivably affect bees when hives are invaded by predators or parasites, when apiculturists transport colonies over long distances, or as an everyday consequence of the busy nature of hives. "Bees bustle around, frequently bumping into each other," he says.
"It's also possible that sleep deprivation could exacerbate colony collapse disorder," he adds, referring to recent alarming declines in bee populations worldwide, "although this hasn't been tested."
Klein and his colleagues devised a method to keep some bees within a colony awake without disturbing the rest of the hive. They attached magnetic steel discs to 25 bees that had been trained to visit a feeder of sucrose solution located 1 kilometre away from the hive. Another 25 trained bees were tagged with non-magnetic copper discs. During the night, while the bees were asleep, a bank of magnets mounted on a rail, called the 'insominator' by the researchers, was passed back and forth along one wall of the hive for 12 hours, jostling the steel-tagged bees and preventing them from dropping off.
The researchers then observed the behaviour of the sleep-deprived bees and their well-rested copper-tagged hive mates for 48 hours, watching a total of 545 waggle dances.
The team found that steel-tagged bees were less able than those with copper tags to indicate the direction from the hive to the feeder (see videos of waggle dances performed by non-sleep deprived and sleep-deprived bees. The correct dance angle is superimposed over the dancer in each case). However, their ability to communicate the distance to the feeder was not significantly affected. "Signalling the direction information may be cognitively or physiologically more taxing than signalling the distance information," suggests Klein.
However, Randolf Menzel, a neurobiologist at the Free University of Berlin who also studies bees, says that the directional sense of bees is known to be partly magnetic. "Changing the magnetic field may disturb their magnetic orientation," he says, "leading to less precision in dance communication."
But Klein is confident that magnetism did not affect the experiment. "We tested for that by comparing the dances between the magnetic steel-tagged bees and the copper-tagged bees on days when the bees had not been sleep-deprived," he says.
Currently a member of the BEEgroup at the University of Würzburg in Germany, Klein says that he would like to investigate whether the bees following the compromised waggle dances can find their way to the feeder. "Is there actually a biologically relevant communication breakdown that translates into less efficient foraging and less competitive colonies?" he wonders