Wasps Seek Safety in Numbers

The family life of many wasp species is stable, highly organized, and utterly strange. Only the queen procreates, while chaste female kin seem content to look after her little ones. But are females really better off rearing a relative's offspring than having their own? In the 20 April Nature, scientists claim that colony life offers celibate handmaidens the equivalent of a life insurance policy.

To study the benefits of social versus solitary behavior, Jeremy Field and his colleagues from University College London studied Liostenogaster flavolineata, a tropical wasp that can do both. Young females can choose to found a nest themselves or remain with their native colony as a celibate helper. The first strategy is risky, says Gavin Shreeves, one of the study's authors, as up to 90% of lone queens will die young, leaving their offspring doomed. Staying at home to rear sisters and nieces is an evolutionary trade-off, because a helper would be certain to pass on some genes, but only those she shares with the queen.

But some researchers wondered if life in an established nest really does offer this guarantee. If a celibate wasp dies, the remaining helpers would have more mouths to feed, raising the odds that more larvae would die. Field's team studied almost 100 Liostenogaster nests, which are plentiful in concrete drainage pipes under forest roads in Malaysia. Each usually houses one queen and up to eight helper females. The researchers simulated the demise of one or two helpers in half of the colonies by removing them from the nests. Surprisingly, larvae in nests with a reduced workforce suffered not much more mortality than those in fully staffed nests.

Somehow the remaining helpers managed to make up for the loss of their colleagues. This means that staying in the nest really is like life insurance; it's costly, but it ensures that some of a helper's genes will be cared for after her death. This benefit may explain why this apparently selfless behavior persists in social insects, Shreeves says.

Evolutionary biologist David Queller from Rice University in Houston, Texas, whose theories on insect social behavior were an important source of inspiration for the British team, is happy to finally see them tested in the field. "It provides the first clear experimental evidence" that it can pay to help rather than procreate, he says.

Posted in Environment, Evolution