Rampant Infanticide Among Mongooses Causes Mothers To All Give Birth On The Same Day
Strict policing and enforcement with possible reprisal could be the way of life for many social animals. While punishments for violations like trespass into wrong territories are norms in most animal societies, a more repressive system forcing mongoose females to give birth at the same time is a little more out-of-the-ordinary, and striking for its fascistic synchronicity.
Michael Cant, an evolutionary biologist at the University of Exeter in the UK, led a team of researchers who looked into how mongooses can adjust their behavior according to the social context. They hypothesized that threat and coercion could be the instruments of compliance in banded mongooses and other social animals. Their study, published in the Proceedings of the National Academy of Sciences, looked at banded mongooses in Uganda, who breed about four times a year. Each group of banded mongooses has the strength of 20 mixed adults dominated by females.
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Cant and his team discovered something very intriguing about the reproductive system in the banded mongoose. The females, according to the researchers, give birth to a communal litter on the same day. In this supposedly egalitarian society, each female would attempt to give birth first so that her offspring were older and fitter compared to the rest in the litter. Oddly enough, the researchers also found that if the females gave birth on different days, the elder pups almost invariably died within the first few days.
The deaths weren't an accident. Older, dominant females in the group were observed to slaughter pups born out of turn. Specifically, when the females are sure that the litter does not include any of her pups, they choose to kill the litter, Cant told iO9.
The researchers hypothesized that the females synchronize their births to escape from this threat of infanticide. The idea is that the when all the pups are born around the same time, murderous females can no longer use temporal or spatial cues to maternity, so they don't kill any of the pups. "Only when the females can be certain that the litter does not contain any of her pups will they kill the litter," Cant explained.
To test their hypothesis, Cant and his team designed an experiment using contraceptive treatment to control the birth in a breeding period. When the subordinate females were not allowed to breed, while only the dominant females bred, all the pups survived their first week - showing subordinate females have no role in infanticide. In the second experiment only one dominant female was allowed to breed. Her litter died within days, - the other dominant females had killed all her pups. A final experiment was designed to allow only subordinate females to breed, which proved to be "a disaster for the litter," Cant said, as all pups died within days because their mothers were subordinate females. In addition, none of these females attempted to breed in the next breeding season, showing the threat proved an effective long-term deterrence.
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