Some parents will do anything to help their own offspring get ahead, even kill other babies. Lions and other pack leaders have earned a fearsome reputation for this, but a new study of meerkats shows that even females further down the pecking order are tempted to murder. The strategy is thought to help expecting mom's pups benefit more from the group's effort to raise them.
Meerkats, a type of mongoose, share parenting duties to an unusual degree. Both males and females babysit while nursing mothers forage and bring pups treats such as beetle larvae. Females will even suckle young that are not their own. But one dominant female in each group monopolizes reproduction, in part by killing the offspring of subordinate females Over 80% of surviving young are her own. When behavioral ecologists Andrew Young and Tim Clutton-Brock of the University of Cambridge, U.K., saw dominant females evicting subordinates from the nesting burrow just before the dominant meerkats gave birth, they suspected the underlings may pose a threat to newborns.
That suspicion turned out to be correct, but it took a long time to prove it. Young, Clutton-Brock, and a cadre of recruited volunteers spent nine years watching meerkats in the Kalahari Desert in South Africa. They tracked the fate of 248 litters among 16 groups. Because pups spend their first few weeks underground, the observers detected their births from the sudden slimming of females. Most pups survived if they were born when no other females were pregnant, but death was likely if a subordinate female was pregnant. Her presence roughly halved the survival chances of a litter belonging to another female, including a dominant one, the team reports in Biology Letters 15 March. Dominant females lost 16 litters during the course of the study; 13 of those failed when a subordinate was pregnant.
A dozen times, observers saw pregnant females drag pups from the burrows, kill them, and eat them. Subordinate females committed half of those infanticides, while dominant females initiated the rest. In two cases, pups killed by subordinates were those of dominant females. The subordinates' share of reproductive success "is likely to be the result of a tactical power struggle among lots of individuals," Young says, and not controlled only by the dominant female.
The finding is fascinating, says behavioral ecologist John Hoogland of the University of Maryland's Center for Environmental Science in Frostburg, because it shows that some of that killing is done by individuals classified as subordinates, a rarity in infanticide among animals. These behaviors have been been difficult to quantify, says Hoogland, who studies infanticide in prairie dogs, but "probably are common within many social species."