Thursday, 1 March 2012

Sleepless Bees

Human babies need a lot of sleep, but as they grow older their body clocks and sleeping habits will change. Other animals also change their body clocks with age. One extreme example is the Honey Bee, Apis mellifera.

The phrase "busy as a bee" is truly deserved in these youngsters. At only 3 days old the infertile females are put to work as "nurse" bees. They feed larvae and are active around the clock without any sleep - for 9 days!

Brains of nurse and forager honey bees were examined for daily rhythms in gene expression (C) Goshzilla Dann, 2008

The infertile honey bee females go through several roles in their lifetime. At 11 days the nurse bees will mature into different worker roles in the hive. At 3 weeks old they become "foragers" with highly rhythmic behaviour: pollen hunting during the day and sleeping at night.

A recent study has looked at the genetics behind the body clocks of the honey bee [1]. They compared the levels of gene expression in the non-rhythmic nurses with the rhythmic foragers. Were there any rhythms remaining in the nurses?

Nurse bees work around the clock without sleep for 9 days (C) Max

The genetic analysis showed that whilst 4% of genes were rhythmic in the foragers brains, only 1.5% were in nurses. Genes in the visual system and the core clock genes did not oscillate in the nurses. However, there were genes involved in energy metabolism that remained rhythmic.

When nurses were taken away from their hive and isolated, they became diurnally rhythmic, being more active during the day. This suggests that their working-around-the-clock behaviour is in part due to their hive environment or association with other bees. However, there are still some underlying rhythms in the nurses that aren't lost even when their behaviour is arrhythmic.

When the nurse bees grow older they take on different roles, as foragers they are highly rhythmic (C) JR Guillaumin

The honey bee represents a useful animal to understand how body clocks can change with age. Like cavefish they show how a body clock can tick quietly in the background. However, I won't be attempting to stay awake for 9 days straight to test this directly!

Enjoy this post? You might also like Old Fruit Flies and Broken Body Clocks and Young or old: who can stay awake better at the wheel?

[1] Rodriguez-Zas, S. L., et al. (2012). Microarray analysis of natural socially regulated plasticity in circadian rhythms of honey bees. Journal of Biological Rhythms, 27(1), 12-24. doi:10.1177/0748730411431404

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