Biological Research

Prenatal Stress in Monkeys

Maternal stress accelerates growth and inhibits motoric development

5. 10. 2016 | Behavioral ecologists from the German Primate Center (DPZ) and the University of Göttingen studied the impact of maternal stress on primate infants in the wild in Thailand. Head of the field project was Prof. Julia Ostner.
At their field station in Thailand, the researchers followed non-human primate mothers through their gestation and their infants through the first one and a half years of their lives. The offspring of mothers that were stressed from food shortages grew faster than their peers but also were affected by slower motoric development and probably a weaker immune system. This is the first study on the effects of prenatal stress in long-lived mammals in their natural habitat. The results support the theory that stressed mothers change their unborn's developmental pace.

It is a known fact that maternal stress often has a long-term impact on the unborn child. Yet, physicians and biologists still discuss whether these maternal influences should generally be regarded as pathological or whether it is an evolved adaptative mechanism. Are mothers able to 'programme' their unborn offspring to increase its evolutionary fitness?

Two young Assamese macaques
Bild vergrößern
(© Kittisak Srithorn )


Two young Assamese macaques | in the northeastern hill evergreen forest of Thailand. The researchers from Göttingen, Germany, conducted their field project in this area. Young macaques whose mothers had experienced stress during pregnancy learned several things later than other youngsters: how to dangle from a branch on one leg later, how to jump backwards or how to leap at least five meters in the canopy of the forest.

This hypothesis is supported by studies on short-lived mammals like rats, since the environmental conditions during gestation are very similar to those the offspring will breed in a few month later. The new study suggests that adaptive prenatal stress effects can also occur in long-lived monkeys. The physiological stress following natural food shortages seemed to cause accelerated growth among young macaques as evident from the analysis of data on fruit availability in the most important tree species, hormone levels in the feces of mothers and growth curves derived from hundreds of photos of Assamese macaque infants in the hill evergreen forest of northeastern Thailand.

Prof. Julia Ostner
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Prof. Julia Ostner
In mammals, growth is usually closely related to important developmental milestones. Andreas Berghänel, the first author of the study, explains: "A shortened life expectancy caused by prenatal development disturbances here leads to an accelerated pace of life. The offspring grows faster and reaches sexual maturity quicker, allowing for earlier and faster reproduction." Even in humans, early life adversities are related to earlier sexual maturity. Nevertheless, Julia Ostner, the head of the field project, is surprised: "The faster pace of life is astounding. We expected that the poor conditions experienced in the womb would have only negative consequences for the young during the gestation period."

And indeed, accelerated growth is only one of the consequences of reduced food availability and an increased glucocorticoid level. Offspring exposed to these conditions showed delayed motoric development and took longer to learn how to dangle from a branch on one leg, to jump backwards or to leap at least five meters far in the canopy of the forest. When an outbreak of conjunctivitis occurred, the external signs were noticed longest in the infants whose mothers had experienced stress during gestation. So also the immune system seems to be affected.

It remains unclear whether the prenatal stress also affected the cognitive development of the offspring. Further investigations are needed to determine whether adverse prenatal conditions increase reproductive rates of macaques and reduce their longevity, as predicted by the hypothesis of the internal adaptive response.
  (© Deutsches Primatenzentrum DPZ, AcademiaNet)

More information

Source

  • Andreas Berghänel, Michael Heistermann, Oliver Schülke and Julia Ostner (2016): Prenatal stress effects in a wild, long-lived primate: predictive adaptive responses in an unpredictable environment. Proceedings of the Royal Society B 20161304. dx.doi.org/10.1098/rspb.2016.1304

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