Right now, bee colonies are suffering dramatic die-offs. This has implications for food security, since we need bees to fertilize a lot of our staple fruit crops, including apples. Now a new scientific study suggests one way to ensure the health of a hive is to make sure its queen is promiscuous.
Photo by Alex Wild
To be precise, a queen needs to mate with at least seven males in order to preserve the colony for as long as possible, in a healthy state. A typical queen might have roughly 14 mates, but if she has fewer than 7, the health of the hive is put in peril. When queens mate, they retain sperm from all their consorts in a special organ, allocating their genetic material over a few years to their daughters. That means a healthy beehive has multiple fathers, and quite a bit of genetic diversity.
North Carolina State entomologist David Tarpy and his colleagues spent a year studying the health and genetic makeup of 3,098 worker bees belonging to 79 colonies. From this study and others in the field, they derived the typical genetic diversity of a colony, as well the survival rates of colonies based on how many fathers had contributed genetic material.
According to a release about the study:
The researchers found that colonies where the queen had mated at least seven times were 2.86 times more likely to survive the 10-month working season. Specifically, 48 percent of colonies with queens who had mated at least seven times were still alive at the end of the season. Only 17 percent of the less genetically diverse colonies survived. “48 percent survival is still an alarmingly low survival rate, but it’s far better than 17 percent,” Tarpy says.
“This study confirms that genetic diversity is enormously important in honey bee populations,” Tarpy says. “And it also offers some guidance to beekeepers about breeding strategies that will help their colonies survive.”
This study could also call into question a few assumptions that have been floated about how colony organisms develop. Specifically, how do animals move from acting as individuals to forming large groups of non-reproductive workers associated with a single queen who does all the egg laying? Biologist William Hughes has written that colony creatures evolved from monogamous mating systems because a monogamous queen would, due to certain quirks of insect genomes, produce sisters who are more closely related to each other than to their possible offspring. Thus, giving up their ability to reproduce isn't as much of a sacrifice, since they can be assured that their genes will be passed on by the queen. Caring for their sisters makes more sense, from a "selfish gene" perspective, than caring for possible offspring.
But this new paper, along with others suggesting polyandry is key to hive health, makes it seem less likely that such social arrangements evolved from hives where there a queen mated with a single male. Such early hives would have been extremely unhealthy and unlikely to survive. Sexual selection, in other words, would favor polyandrous queens over monogamous ones.