Being a good parent can shorten your life, according to researchers working on a species of burying beetle at Cambridge University.
Burying beetles are unusual because they care for their young. They locate the body of a small bird or mouse, strip the body of feathers or fur, and bury it to create an edible nest in which their larvae are raised.
Left alone, the larvae can fend for themselves by eating the nest. But the parents can also provide input by helping the young to feed.
To find out how these two different rearing strategies affect both the offspring and the parents, Rebecca Kilner, who led the study, bred two groups of beetles. One group was allowed to be "good" parents and help their larvae to feed. In the second group, the parents were removed, leaving the larvae to their own devices. This was the "bad" parent group.
Larvae that received good levels of care, she found, grew up to be good parents themselves, whereas those who had poor levels of care became bad parents and so did their offspring.
To judge what made a "good" beetle parent, the team measured the size and number of the larvae a beetle produced. They also measured the fitness cost of parenthood on the beetle by assessing how long it lived after caring for the larvae. Parents paired together from the good quality group had a lot of larvae and then lived for a long time, whereas those "bad" pairings had a few scrawny larvae and died quickly afterwards.
But then they investigated what happened when a good parent was paired with a bad parent. Their work, published in eLife this week, shows that, in these pairings, the good parent suffered and had a shorter lifespan than if it were paired with another good quality parent.
This is probably because the edible nest built by the beetles also acts as a food source for the parents as well as their offspring. So parents need to balance how much of this this food they share with the larvae against their own needs to cover their personal cost of parenting.
Paired with a bad parent, the good parents worked harder than they would have done if they were paired with another good parent and did not feed sufficiently to recover. Kilner dubbs these beetles as "sacrificing themselves for the good of the young."
What surprised the researchers was the rapidity with which the effects of a change in the rearing environment was passed on to subsequent generations. This might, they suggest, have implications as to how fast evolution might work.
"If the rate of evolution can, under some conditions, proceed more quickly, some populations may be able to survive and adapt" to challenging conditions in the environment, Kilner points out.