The researchers examined a behavior in honey bees known to regulate the social behavior of the hive – the retinue response. Retinue response is the amount of time and attention worker bees pay to the queen because of a special pheromone or chemical she sends out. This chemical keeps the hive socially connected. In any group of animals, individuals will behave differently. Some worker responses have a very high retinue response – spending a lot time very close to the queen and picking up the pheromone; and some others have a very low retinue response. The authors set out to measure the amount of individual differences in behavioral and physiological (internal body function) responses to queen pheromones.
Normally, the Queen pheromone is spread over the hive by daughter worker bees. However, there are some worker bees who either don’t prefer the pheromone or avoid the queen altogether. When that happens, physiological changes occur and these daughters have somewhat developed ovaries. These stand-offish daughters have been known to lay their own eggs (usually a no-no in polite Hymenopteran society) which can develop into reproductively capable sons. That doesn’t often happen because other sisters who find nephews (and not brothers) in the bee nursery have been known to discard or destroy the eggs or pupae.
Worker honey bees from two different sub-species (or races): Carniolan and Italian bees were observed. These are very old and well-known races of bees that are morphologically distinct (different physical appearance and shape). The researchers studied 5 colonies of the Carniolan bees and 4 colonies of the Italian bees.
Drops of diluted queen pheromone were placed on a slide and introduced to smaller groups of bees (from each colony). The researchers counted the number of worker bees that came into contact with the pheromone and the number of times each bee visited the slide over a period of time (25 minutes). They did this for 5 consecutive days, doing it in the spring and again in the fall.
What did they find?
So what could be driving these differences? Like I mentioned before, all of study bees were full sisters to each other so it can’t be the genes, right? Well, not quite. The researchers did identify the genes they believe responsible for retinue response. What they found was that although the sisters may have been similar to each other in the types of genes they had, gene expression differed from bee to bee. It’s one thing to have the same gene as another person. It’s something else to have that gene actually work and perform in your body. The same gene in your body may do more work (or less work) than that same gene does in my body. This is called individual variation in genetic expression and that is what seems to be at play with the bees. Retinue response is correlated to ovarian development which is correlated to gene expression.
Why does any of this matter?
Full Citation: Kocher SD, Ayroles JF, Stone EA, & Grozinger CM (2010). Individual variation in pheromone response correlates with reproductive traits and brain gene expression in worker honey bees. PloS one, 5 (2) PMID: 20161742
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