This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Female mandrills are more likely to experience pregnancy loss when they are simultaneously nursing an infant, which may reflect a physiological trade-off between current and future offspring, according to a study by Nikolaos Smit at the Max Planck Institute for Evolutionary Anthropology, Germany, and the University of Turku, Finland, and colleagues, published in PLOS Biology. Pregnancy and nursing are physically demanding tasks, so female mammals must allocate their resources carefully to maximize their reproductive success.
When a pregnant female is simultaneously nursing an infant, it creates a trade-off between the needs of their current offspring and their developing fetus. To investigate how females adapt to these conflicting physiological demands, researchers observed the behavior and reproductive lives of a wild population of mandrills (Mandrillus sphinx) in southern Gabon. Mandrills breed seasonally and females usually conceive every other year but can sometimes become pregnant again while still caring for an infant.
Pregnant female mandrills have visible swellings, enabling the researchers to record both successful and failed pregnancies. During the 11-year study, they observed 356 pregnancies across 117 females, involving 52 instances of fetal loss. They found that fetal loss was more common in females that were simultaneously caring for an infant.
Females were also more likely to experience fetal loss when their infant threw more 'tantrums,' characterized by distinctive distress vocalizations, or when there were more alpha male takeovers in their social group during the pregnancy. However, females who experienced fetal loss tended to conceive again sooner and produced more surviving offspring overall compared to females whose infants died soon after birth. In the long term, females that lost a pregnancy produced a similar number of surviving offspring as females that had not.
These findings suggest that fetal loss may be a physiological response to the extra energetic demands of simultaneous pregnancy and nursing, enabling mothers to focus on the survival of their current offspring. It may also reduce the physical costs to the mother when she is unable to sustain a pregnancy, enabling her to reproduce again sooner once her current offspring has reached independence. The correlation between alpha male changeover and fetal loss could represent an adaptation to the increased risk of infanticide by new alpha males, or may reflect increased stress for females during times of social upheaval, the authors say.
First author Smit states, "We combined 11 years of reproductive histories with noninvasive observations of pregnancy and detailed behavioral observations of mothers and infants. This unique combination of long-term demographic and behavioral data allowed us to uncover links between infant behavior, maternal investment and subsequent reproduction that would otherwise be difficult to detect. "Females who conceive while caring for a dependent infant are more likely to experience fetal loss, especially when this infant has been showing more tantrum behavior." Senior author Marie Charpentier adds, "Fetal loss is usually seen as a reproductive failure.
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