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 | 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.
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)