In social insects, like honey bees, the queen is usually the only one making babies. All other females are subordinate and sterile.The reason natural selection doesn’t weed out this behavior is thought to be because all the subordinate females are nearly genetically identical to the queen. In other words, as long as the queen is passing on her own genes, the genes of the workers get passed on, too.
But what about social insects where unrelated individuals are found in the nest? How do they benefit from being subordinate and not reproducing? New research on a species of social wasps, the European paper wasp Polistes dominula, reminds us that things are not always as they first appear. The research was published in the August 12, 2011 issue of the journal Science.
They found that invading females who wait around long enough often get lucky and inherit the colony. These females seem to have the right strategy, since they wouldn’t fare as well if they just tried to up and start their own colony in the first place. No, this isn’t any feel-good story about altruism in the animal kingdom. It’s just plain old opportunism.
Female paper wasps start their colonies in the spring, either alone or with a small group of other founder females. But only one girl can be the boss. She lays most or all of the eggs while the others gather food for her offspring. How nice of them to help out, right?
You might think that these other females are probably close relatives of the boss lady, but as it turns out, 15-35% of these co-founders are unrelated to the dominant female. On the surface, it seems like these wasps are doing quite a bit of work for no reward. In fact, even co-founders that are full sisters of the dominant founder get basically nothing out of the deal; the help they provide doesn’t result in that many more offspring from the dominant female. They would apparently be better off just founding their own nests. So why do these wasps “help”?
What the researchers discovered was that “helping” females are just biding their time. Colonies are founded in the spring and disperse in late summer when the queen dies. If she makes it that long. In the wild, there’s a decent chance that the boss lady will die before the end of the breeding season, after she’s put in all that work to start a colony and ascend the throne. When that happens, a new queen can emerge, and it doesn’t have to be someone related to the old queen.
How often does this happen? The authors estimate that 87% of the time, the original dominant female makes it through the whole season. But, for females that wait around to see if she dies, the payoff is huge.
From the standpoint of a female wasp, it’s better to save resources and reproduce later in the season. This is because eggs laid earlier in the season hatch into non-reproductive, subordinate females. These are the workers and have no chance of contributing to the next generation. You need them around to help raise all the future queens that come later, but frankly they’re kind of a waste of eggs. Females that inherit a nest after the dominant female dies can save up their eggs for later, when the reproductive females and males will be produced.
In the meantime, subordinate females can sneak in a few eggs on the sly, especially in larger groups of co-founders. About 32% of the offspring from subordinate females in the study came from eggs that were laid before the dominant female died. But, for the most part, they waited their turn.
The craziest part about this study is how many wasps were studied. First of all, the authors had to paint markings on individual wasps, so they could follow them throughout the study, and then extract DNA from a tiny piece of wasp leg so they could determine which babies had which baby mamas. They did this 4 times during the breeding season, sampling individuals from 17-22 nests each time. That’s a lot of wasp collecting.
But that’s not all! They then wanted to track which female offspring would go on to found their own nests, and which ones were just workers. For this, they used a separate set of 145 nests and marked all the emerging offspring every 6 days once they started to emerge. They then returned the next year in March to search for the marked females. That is serious commitment to research.
As the results of the study (and its publication in Science) show, good things come to those that wait.
Leadbeater, E., Carruthers, J., Green, J., Rosser, N., & Field, J. (2011). Nest Inheritance Is the Missing Source of Direct Fitness in a Primitively Eusocial Insect Science, 333 (6044), 874-876 DOI: 10.1126/science.1205140