Queen bees took time to play the field, scientists say
Queen bees only became polygamous once they were confident — evolutionarily speaking — that their offspring would be taken care of by the hive, say U.K. and Australian researchers.
Behavioural ecologist Associate Professor Madeleine Beekman of the University of Sydney and colleagues reported their findings in Friday's issue of the journal Science.
The researchers compared the mating behaviour of 267 species of bees, wasps and ants that live together in highly co-operative societies. They found that in older species, females were always monogamous and that species with polygamous females, such as queen honey bees, evolved relatively recently.
The findings add weight to one explanation for a long-standing evolutionary paradox — why do some individuals of a species altruistically look after someone else's offspring?
According to Charles Darwin's theory of natural selection individuals aim to have as many of their own offspring as possible, or at least more offspring than their neighbour, in order to ensure the propagation of their genes. So how can a trait that causes sterility, which is present in worker honey bees, spread in a population?
One popular explanation has been that helping to rear the offspring of relatives, rather than reproducing personally, is an effective way of passing on your genes. But this "kin selection" theory has been challenged by, among others, the eminent biologist E.O. Wilson, the founder of sociobiology, who argue that relatedness doesn't matter and that insects evolve social behaviour because it makes life easier for them.
Those challenging kin selection point to honey bees to show that co-operative child care exists even when the offspring aren't highly related, because they are the product of the queen mating with many males.
But, says Beekman, honey bees evolved relatively late and the females of species that evolved earlier were monogamous.
This supported the kin selection theory that co-operative societies evolved when the offspring were related and only then did multiple mating evolve.
"Females had to refrain from multiple mating in order for sociality to evolve," says Beekman.
Over time, sociality led to the specialized roles seen in honey bees, in which the egg-laying queen and worker bees that care for the young are highly dependent on each other.
"Once that point had been reached in evolution, the queen could do whatever she wanted, like mate with more than one male," Beekman said.
The workers may no longer have the evolutionary incentive to look after the queen's offspring, but by that stage they had no option because they were sterile.
Mating between the queen and a number of males provides the advantages of genetic diversity in the colony, says Beekman. She says genetic diversity is believed to make the colony more resistant to disease and also allow for worker bees from different fathers, who have different strengths and weaknesses, to have specialized roles in the colony.