As part of a long-term study of wild vervet monkeys using state-of-the-art bio-logging technology, research by Nottingham Trent University has for the first time recorded the birth temperatures of wild primates.
The research is testing traditional ideas about why monkeys that are active during the day evolved to give birth at night. Night birth has long been considered a predator avoidance strategy or a way for mothers to recover from birth and bond with the child without interference from other apes or troop movements.
Over seven years, 17 births that occurred during an inactive nocturnal phase were analyzed. Two day births were also observed and examined.
Laboring females have been observed to have lower nocturnal body temperatures than non-laboring females and reach these temperatures earlier in the night. Whelping females also experienced lower temperatures during birth than during the night of the previous seven days.
For both daytime births, the researchers identified a drop in maternal body temperature before delivery, immediately followed by a rapid rise.
Dr. Richard McFarland, a lecturer in psychology at NTU’s School of Social Sciences, has spent nearly a decade studying the thermoregulation of primates in South Africa, including the impact of climate on their behavior. He said: “Our results suggest that there may be important thermal consequences related to the timing of birth in primates.
“We have observed that a mother’s body temperature drops at birth to create a cooler thermal environment that serves to protect the fetus from injury during hypoxic delivery conditions. Immediately after birth is also a critical period for the infant, where the newborn may be at risk of hypothermia if they are born on a cold night, or at risk of hyperthermia if they are born during the heat of the day. The physiology of the mother and her behavior towards the child are essential during this period.
“Birthing at night maximizes the thermal efficiency of the birthing process, making it easier for the mother to lower her body temperature at birth, in conditions that tend to be cooler. It would be physiologically more difficult to deliver during the heat of the day, when the mother’s body temperature is naturally higher.
“Additionally, during the night, the mother does not need to implement evaporative cooling to lower her temperature and can instead rely on less expensive dry heat loss. In a time when maternal resources are scarce, all means by which resources can be conserved and physiological processes made less costly are likely to improve the well-being of mother and child.”
Vervet monkeys are also known to consume the placenta after birth, which has previously been claimed to replenish nutritional losses of pregnancy, reduce pain, and prevent the placenta from attracting predators. Researchers now suggest it may also provide the energy needed to recover temperature after birth.
The study findings have broad implications for both understanding primate reproduction and human birth patterns and health risks.
Dr McFarland added: “It seems reasonable to suggest that timing of birth will be particularly important for smaller and more heat-vulnerable species, where birth should be more synchronized with the most thermally advantageous time. This may explain why monkeys are less engaged. at night birth than monkeys.
“Humans, like apes, tend to give birth more frequently at night, but not as regularly as other non-human primates. Greater flexibility in the timing of human births is likely a consequence of our reliance on medical intervention , including artificial birthplace environments and a greater reliance on hospital deliveries and medical intervention.Nevertheless, the risk of neonatal hypothermia, in particular, remains an important cause of morbidity and mortality children, especially in developing countries and during the winter months.
The article The thermal consequences of primate birth time and its evolutionary implications was published in the journal Royal Society Biology Letters.
Richard McFarland et al, The thermal consequences of primate birth time and its evolutionary implications, Biology Letters (2022). DOI: 10.1098/rsbl.2021.0574
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