Bruce effect

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The Bruce effect is a form of premature termination of pregnancy that occurs in mammals when the female comes into contact with the smell of a strange male. The effect is known in at least 12 species of rodents , the best known of which is in the house mouse . It is named after Hilda M. Bruce , who discovered this connection in 1959.

The Bruce effect is triggered by an olfactory stimulus - i.e. via the sense of smell. In mice, perceiving the urine of a strange male is sufficient. The hormone prolactin is reduced in the female , while the estrogen level is increased, which prevents the growth of the uterine mucosa and makes nidation of the blastocyst impossible, ultimately resulting in a miscarriage . This “pregnancy block” is particularly effective when an unknown male is brought to the pregnant female. The effect can only be seen in the first three days of pregnancy. After that, the pheromones from the male no longer have any effect.

Since there is hardly any evidence of this effect in wild animals, it is however controversial whether this is an artifact that only occurs under laboratory conditions . However, in February 2012 researchers from the University of Michigan published a study that is said to be the first to provide comprehensive evidence of the Bruce effect in wild animals. In the case of blood breast baboons ( Theropithecus gelada ) from the Ethiopian Simien National Park, 80% of the pregnancies were terminated within one week after the dominant male was replaced. Furthermore, data on the birth intervals of females suggest that such an abortion can increase the reproductive success of a female whose offspring would otherwise be at risk of infanticide . The Bruce effect could thus be an evolutionary developed strategy of the females. In addition, by triggering the abortions, the males ensure that they can reproduce more frequently, as the females are now able to have young again from the “new” male - similar to the lions - or the male langurs , which are often the young of females kill when they join a new pack.

literature

  • Wilfried Westheide, Reinhard Rieger: Special Zoology. Part 2: vertebrates or skulls. Spectrum Akademischer Verlag, Heidelberg 2004, ISBN 3-8274-0900-4

Individual evidence

  1. ↑ Hilda M. Bruce: An Exteroceptive Block to Pregnancy in the Mouse. In: Nature . 184/105, July 11, 1959, doi: 10.1038 / 184105a0
  2. ↑ Jerry. O. Wolff: Laboratory Studies with Rodents: Facts or Artifacts? In: BioScience. Vol. 53 (2003), No. 4, pp. 421–427, ( abstract )
  3. ^ Eila K. Roberts, Amy Lu, Thore J. Bergman & Jacinta C. Beehner: A Bruce Effect in Wild Geladas. In: Science . February 23, 2012, doi: 10.1126 / science.1213600
  4. ^ Spiegel Online: Baboons: New boss causes miscarriages . February 24, 2012
  5. ^ R. Dawkins: The Selfish Gen. 1976, p. 147 (2006 edition, ISBN 978-0-19-929114-4 ).