Failing memory is one of the most distressing symptoms of old age. We forget things and learning new tasks becomes difficult. But we are not the only species to suffer such problems; ageing fruitflies, zebrafish and worms also lose the ability to learn and retain memories. Yet bees take on new responsibilities in the hive as they age, graduating from tending the brood when young to foraging during their last few weeks. It seems that older bees can learn new tricks, which made Ricarda Scheiner and Gro Amdam wonder how bees' memories fare, but not with age alone: as the insects' roles change. They wondered how foragers' memories compared with nurses', but to find out they'd have to compare insects of the same age. Fortunately, Scheiner explains that it is possible to trick some young bees into taking foraging roles, even though they are the same age as nurses, so Scheiner and Amdam decided to test identically aged foragers and nurses to find out how their roles affect their memories (p. 994).
Despite working in the heart of Berlin, Scheiner has no problems keeping her bees happy. `Berlin is a very green city,' she says, `the city's bee keepers get 20% more honey from their hives than bee keepers in the surrounding countryside'. Taking brood combs from her city centre hives,Scheiner collected young bees each day, as they emerged from the brood combs,and installed them in separate mini-hives to found new communities where all of the inhabitants had identical ages. Supplying each new nest with a queen,some honey, pollen and brood, the youngsters soon coalesced into a new community and establish their roles. Scheiner was ready to test the insect's memories.
Focusing on the insects' abilities to learn new tasks, Scheiner trained the insects to extend their proboscises whenever they stroked their antennae across a metal grating engraved with a specific pattern. Comparing nurses with young foragers that had been gathering food for less than 13 days, the two groups seemed to learn the task equally well with 63% of the nurses and 73% of the recently fledged foragers learning the task. However, the longer-term foragers, who had been out foraging for at least 15 days, didn't learn as well. Only 46% of the veterans learned the task, compared with 73% of nurses of the same age. Scheiner suspects that the veteran foragers' brains had deteriorated significantly compared with their nurse nest mates who had never left the nest. So the length of time that a bee has been foraging has a big impact on her ability to learn new tricks.
However, when Scheiner tested the insects' long-term memories, she was in for a surprise. Comparing the experienced and less experienced foragers'memories with nurse bees of the same age, there was no difference between the foragers' and nurses' abilities to remember to stick out their tongues. Their memories were equally good. Even more surprisingly, by the time 3 days had passed the veteran foragers' memories were better than the nurses' and younger foragers'. Even though the veterans found it more difficult to learn, they retained the memory better than the young foragers.
Having found that a bee's role has a big impact on its brain function,Scheiner is keen to understand the differences between veteran foragers' and nurses' brains with the hope of one day understanding more about the mechanisms of memory loss in ageing human populations.