Acts of apparent altruism in European paper wasps can be explained by plain old self-interest, a new study finds.
Polistes dominulus females can either establish their own nests to raise young or join other females for joint homemaking. In those joint nests, though, one female fights her way to the top and does most of the egg-laying while the others do most of the drudge work in taking care of the top wasp’s young.
When a subordinate helps her sister, that’s not hard to explain: The underling may not end up with her own offspring, but her reproductive success includes an indirect share of her sister’s brood, because relatives share genes. Forgoing her own direct offspring counts as a kind of altruism, in which an individual helping kin trades direct for indirect benefit. Either way, the wasp’s self-interest is served.
But some 15 to 35 percent of co-queens slaving away are not closely related to the top wasp, so biologists have been puzzled about why those strangely helpful females don’t go off to found their own nests.
They do it because joining an unrelated queen’s nest offers a chance of grabbing the throne, says Ellouise Leadbeater of the Zoological Society of London. She and her colleagues tracked the fortunes of 1,113 foundresses in 228 nests in southern Spain.
In this epic population analysis, females that started out as subordinates to a nonrelative occasionally took over the whole nest and laid their own eggs. Their triumphs were rare but dramatic enough so that, overall, the strategy worked out better than being a single mom: Lone nest foundresses hardly managed to produce any offspring, the researchers report in the Aug. 12 Science.
“What is interesting and important about this study is that it demonstrates very clearly that inheritance of colonies can explain why subordinates occur and help on nests of nonrelatives,” says Joan Strassmann of Washington University in St. Louis. In 2000, she and her colleagues first described the puzzling female wasps who choose to help at strangers’ nests instead of founding their own.
“People have too quickly jumped to the conclusion that just because animals help each other, they are behaving altruistically,” says Raghavendra Gadagkar of Indian Institute of Science in Bangalore. The new study, he says, may inspire closer looks.
