Some people might suggest that the inside of an embalmed corpse is no place to bring up a small child. Looking after babies is an exhausting, smelly business at the best of times, but the dead body of a small rodent means one thing to a pair of burying beetles (Nicrophorus vespilloides): the perfect place to raise a family. Converting the carcass into a hidden underground ‘crypt’, the beetles regurgitate meat to their young, until they mature.
The peculiarities of burying beetle parenting go further than their choice of nursery, however. Unusually for insects, both males and females undertake the task of caring for their young. But confusingly, the male stays in the crypt even when he is of no further benefit to his young. If he could safely leave to find new mates, instead of helping this one, why does he stay?
Vicky Jenkins and colleagues at Edinburgh University studied this question by setting up both single mother and biparental families, and measuring the size of the resulting offspring. They then allowed females from both groups to raise a second brood, this time without the help of a male. They found, as expected, that the young from biparental families were no bigger than those raised by a lone female. But in their subsequent attempt, females who had previously had help produced a bigger, better brood.
“In the wild, females often raise a brood alone, using sperm stored from a previous mating,” Jenkins explains. “Even if a female later mates with another male, a proportion of her offspring might be fathered by the first male because his sperm is still there.” By sharing the exhausting jobs of feeding and protecting the young, a male leaves his mate with more energy to raise a second brood, some of which could be his.