Infanticide common among adult males in many mammal species

WASHINGTON (Reuters) - Predators such as leopards and cheetahs are not the biggest mortal threat to baby Chacma baboons, large and aggressive monkeys that live across southern Africa. That threat comes from adult males of their own species.

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“Up to 50 percent of the infants might be killed by males in these populations, a massive impact more important than disease or predation,” University of Cambridge behavioral ecologist Dieter Lukas said.

This behavior is not limited to these baboons. Scientists on Thursday unveiled the most detailed study to date of infanticide by adult males among the world’s mammals, a practice documented in numerous species including many primates.

The researchers studied 260 species including 119 that practice infanticide and 141 that do not, looking for patterns that may explain a behavior seen in very few non-mammals.

“It is a sexual strategy,” said behavioral ecologist Elise Huchard of the National Center for Scientific Research’s Center for Evolutionary and Functional Ecology in France, who with Lukas conducted the study published in the journal Science.

Huchard said males kill babies fathered by others to make the dead infant’s mother available for mating. Huchard estimated infanticide occurs in about 25 percent of mammals.

Mammals in which infanticide is common typically live in groups - as do Chacma baboons - in which reproduction is monopolized by a small number of males that often cannot keep their dominant position for long due to many challengers. Infanticide is rare in solitary or monogamous mammal species.

Infanticide was found to be widespread, occurring in rodents including mice and squirrels, carnivores including lions and bears as well as in hippos, horses and even the white-throated round-eared bat. Many primates practice infanticide including chimpanzees, gorillas, baboons and langurs while others do not, including orangutans, bonobos and mouse lemurs.

The researchers said females of some species use strategic promiscuity to stop males from killing their babies. By mating with as many males as possible in a short time, they make it hard to discern infant paternity.

“Males stop killing offspring if there is a risk that the offspring might be their own,” Lukas said.

Infanticide was not seen in mammals with seasonal reproduction because there is no benefit to males that still would need to wait until the following breeding season for females to become fertile again.

“Infanticide by males repeatedly evolved in lineages in which males fight over access to groups of females and where females can give birth throughout the year,” Lukas said.

Reporting by Will Dunham; Editing by Sandra Maler