Bruce effect

The Bruce effect is a occurring in mammals form of premature termination of pregnancy in the female contact with the odor of a strange male. The effect is known to exist in at least 12 species of rodents, most famously, he is in the house mouse. It is named after Hilda M. Bruce, who discovered this relationship in 1959.

The Bruce effect is triggered by an olfactory stimulus - that is about the sense of smell. In mice, the perception of the urine of a strange male is sufficient. The female hormone prolactin, estrogen levels Reduction is increased, however, which prevents the growth of the uterine lining and makes the implantation of the blastocyst impossible, finally followed by a miscarriage. This " Gestational blocking " is particularly effective when an unknown male is brought to pregnant females. The effect is observed only in the first three days of pregnancy. After originating from the male pheromones are no longer effective.

Since there is little evidence of free-ranging animals for this effect, but it is debatable whether this is not an artifact occurring only under laboratory conditions. However, in February 2012 published researchers from the University of Michigan, a study is expected to provide comprehensive evidence of the Bruce effect in wildlife for the first time. Here in blood chest baboons ( Theropithecus gelada ) were discontinued from the Ethiopian Sämen National Park 80 % of pregnancies within a week after the dominant male was replaced. Continue to place data close to the birth intervals of females that such a termination of pregnancy may increase the reproductive success of a female, whose descendants would otherwise infantizidgefährdet. The Bruce effect may thus be an evolutionarily developed strategy of the females. In addition, the males make by triggering the abortions that they can themselves reproduce more frequently as females are now again able to get boy of the "new" male - similar to lions or Langurenmännchen that often the young animals kill the females when they come in a new pack.