Female mandrills are more likely to miscarry when they become pregnant while still caring for a dependent infant, and the risk rises when that infant makes more persistent demands for care, according to a study led by scientists from the Institute of Evolutionary Science in Montpellier, the University of Turku and the Max Planck Institute for Evolutionary Anthropology. The researchers say the pattern suggests fetal loss may sometimes form part of a broader reproductive strategy, helping mothers balance investment between current and future offspring.
The study, reported by the Max Planck Society, analysed 356 pregnancies in 117 wild female mandrills monitored over 11 years. The data came from the Mandrillus Project and cover the only habituated population of wild mandrills, allowing researchers to observe individuals over many years and record both reproductive outcomes and detailed social behaviour.
The researchers describe a fundamental trade-off for mammalian mothers: how to divide limited energy and resources between existing offspring and those yet to be born. The conflict is especially demanding when a female conceives while her previous infant still depends on her for milk, protection and care. Fetal loss occurs in an estimated 10 to 20 per cent of primate pregnancies, including those of humans and non-human primates, but the study notes that its causes and consequences in natural populations are not well understood.
Females that conceived while still caring for dependent young were more likely to miscarry than females without dependent offspring. Pregnant females with dependent young were also more likely to reject their infants' demands for care, and fetal loss was more likely when the offspring showed more protest behaviours, such as persistent demands for maternal care.
The study also examined what followed a miscarriage. In the medium term, females that lost a fetus had better reproductive outcomes than females that gave birth and then lost their newborn. Females that had experienced fetal loss ultimately produced more offspring that survived to adulthood and had shorter intervals between births than females whose infants died after birth. The authors suggest fetal loss may be a physiological response to an early pregnancy at a time when the mother is still heavily investing in a dependent offspring, and may reduce the costs of carrying a pregnancy unlikely to result in a successfully weaned young.
"We combined over a decade's worth of observations on reproductive histories with non-invasive observations of pregnancies, as well as detailed behavioural observations of mothers and infants," said lead author Nikolaos Smit, a postdoctoral fellow at the University of Turku who was formerly based at the Max Planck Institute for Evolutionary Anthropology. "This unique combination of long-term demographic and behavioural data enabled us to reveal connections between infant behaviour, maternal investment and subsequent reproduction that would otherwise have been challenging to identify."
Marie Charpentier, director of the Mandrillus Project, which provided the data, said: "Fetal loss is typically considered a form of reproductive failure. Our findings suggest that, when females are already investing heavily in a dependent infant, this may be a way of adjusting investment between current and future offspring."
The authors link the behaviour of the young to a conflict of interests between mother and offspring: the infant continues to demand care, while the mother may benefit from reducing her investment in it to focus on future reproduction. Offspring that protest more, the researchers suggest, may impose higher energetic or social costs on their mothers, particularly during pregnancy.
Analysis
Why This Matters
- The study offers an explanation for miscarriage that frames it as part of a reproductive trade-off rather than only a failure, a question the authors say is poorly understood in wild populations.
- It connects an infant's behaviour, such as persistent demands for care, to a physiological outcome in the mother, a link the researchers say long-term demographic and behavioural data made visible.
- It adds evidence to the idea that the timing and spacing of births is shaped by the mother's competing investment in offspring already born and those to come.
Background
Mandrills are primates native to the forests of Central Africa, and females raise their young over an extended period of dependency. Because a female can conceive again while an earlier infant still relies on her, the species is well suited to studying how mothers divide limited resources between offspring. Fetal loss is common across primates, but in wild populations its causes and consequences are difficult to observe, which is why long-running monitoring of identifiable individuals is central to this kind of research.
Key Perspectives
Marie Charpentier, director of the Mandrillus Project: says fetal loss is typically considered a form of reproductive failure, but that the findings suggest it may be a way of adjusting investment between current and future offspring when a female is already investing heavily in a dependent infant.
Nikolaos Smit, lead author: says combining more than a decade of observations on reproductive histories with non-invasive observations of pregnancies and detailed behavioural observations enabled the team to reveal connections between infant behaviour, maternal investment and subsequent reproduction that would otherwise have been hard to identify.
What to Watch
- Whether the proposed physiological mechanism behind fetal loss in these circumstances is taken up in further studies of the same monitored population.
- Whether the pattern linking infant protest behaviour to pregnancy outcomes is tested in other long-term primate datasets.
- How the interpretation of fetal loss as a possible adaptive adjustment is received in reproductive biology and primatology, given the authors' own framing of it as a departure from the usual view.
Checked
12 claims in this story checked against 1 source: 12 supported.
Show each claim
- SupportedFemale mandrills are more likely to miscarry when pregnant while caring for a dependent infant.Max Planck Society - Research.: “Female mandrills that become pregnant while still caring for dependent offspring are more likely to miscarry.”
- SupportedFetal loss may sometimes help mothers adjust investment between current and future offspring, rather than being only reproductive failure.Max Planck Society - Research.: “Rather than merely representing reproductive failure, miscarriage may reduce the costs associated with carrying a pregnancy that is unlikely to result in a successfully weaned young.”
- SupportedThe study draws on 11 years of data from the only habituated population of wild mandrills.Max Planck Society - Research.: “The study has been based on the only habituated population of wild mandrills”
- SupportedThe research was led by scientists from the Institute of Evolutionary Science in Montpellier, the University of Turku and the Max Planck Institute for Evolutionary Anthropology.Max Planck Society - Research.: “Led by scientists from the Institute of Evolutionary Science in Montpellier, the University of Turku and the Max Planck Institute for Evolutionary Anthropology”
- SupportedResearchers analysed 356 pregnancies in 117 wild female mandrills monitored for 11 years.Max Planck Society - Research.: “researchers analysed 356 pregnancies in 117 wild female mandrills that had been monitored for 11 years.”
- SupportedFetal loss was more likely when dependent offspring exhibited more protest behaviours.Max Planck Society - Research.: “Notably, fetal loss was more likely when the offspring exhibited more protest behaviours.”
- SupportedSmit said, “We combined over a decade’s worth of observations on reproductive histories with non-invasive observations of pregnancies, as well as detailed behavioural observations of mothers and infants.”Max Planck Society - Research.: ““We combined over a decade’s worth of observations on reproductive histories with non-invasive observations of pregnancies, as well as detailed behavioural observations of mothers and infants,” says lead author Nikolaos Smit”
- SupportedPregnant females with dependent offspring were more likely to reject their infants’ demands for care.Max Planck Society - Research.: “Pregnant females with dependent offspring were also more likely to reject their infants' demands for care.”
- SupportedFetal loss occurs in an estimated 10 to 20 per cent of primate pregnancies, including human and non-human primates.Max Planck Society - Research.: “Fetal loss occurs in an estimated 10 to 20 per cent of primate pregnancies, including those of humans and non-human primates.”
- SupportedFemales that lost a fetus had better reproductive outcomes in the medium term than females that gave birth and then lost their newborn.Max Planck Society - Research.: “In the medium term, females that lost a fetus experienced better reproductive outcomes than females that gave birth and then lost their newborn.”
- SupportedFemales that experienced fetal loss ultimately produced more offspring that survived to adulthood and had shorter intervals between births than females whose infants died after birth.Max Planck Society - Research.: “females that had experienced fetal loss ultimately produced more offspring that survived to adulthood and had shorter intervals between births than females whose infants died after birth.”
- SupportedCharpentier said, “Our findings suggest that, when females are already investing heavily in a dependent infant, this may be a way of adjusting investment between current and future offspring.”Max Planck Society - Research.: ““Our findings suggest that, when females are already investing heavily in a dependent infant, this may be a way of adjusting investment between current and future offspring.””
