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The Bruce effect is a form of pregnancy disruption in mammals
in which exposure of a female to an unknown male results
in pre- (Bruce 1959) or postimplantation failure (e.g.,
Storey and Snow 1990).
Some form of pregnancy block or disruption
has been reported in the laboratory for at least 12
species of rodents, including domestic mice,Mus musculus; deer mice,
Peromyscus; and vole, Microtus (reviewed in Mahady and Wolff 2002).
The basic design of these experiments
is that a recently inseminated female is exposed directly
to an unfamiliar, nonsire male or to its urine or soiled
bedding,which in turn causes her to prevent implantation or
to abort or reabsorb her embryos. Pregnancy disruption may
occur at any time from conception to 17 days postmating, depending
on the species and experimental conditions (e.g.,
Stehn and Richmond 1975, Stehn and Jannett 1981, Storey
1994).
Variables such as length of exposure, timing of exposure
to a strange male, sexual experience, and behavior of
strange males may all influence the degree of pregnancy failure
(e.g., Stehn and Richmond 1975, Kenney et al. 1977,
Storey and Snow 1990). The overall implication is that some
level of exposure to strange males disrupts normal pregnancy
in female rodents. This response supposedly is adaptive for the male, in that termination of pregnancy results in the female
coming into estrus within 1 to 4 days, providing the male
with a mating opportunity.
The benefit to the female is less
clear, but if the strange male were to commit infanticide and
kill her offspring after parturition, a female could conserve reproductive
effort by aborting her current litter and mating
with the new male (Schwagmeyer 1979). Thus, pregnancy
block, or termination of pregnancy, supposedly evolved as a
female counterstrategy to infanticide by males.
The Bruce effect has repeatedly been tested outside the laboratory, but only little supporting evidence could be found (e.g. de la Maza et al 1999).
So the Bruce effect might be a laboratory artefact.
Literature:
-Bruce HM.1959. An exteroceptive block to pregnancy in the mouse.Nature
184: 105.
-Storey AE, Snow DT. 1990. Postimplantation pregnancy disruptions in
meadow voles: Relationship to variation in male sexual and aggressive
behavior. Physiology and Behaviour 47: 1925.
-Mahady S,Wolff JO. 2002.A field test of the Bruce effect in the monogamous
prairie vole,Microtus ochrogaster. Behavioral Ecology and Sociobiology
52: 3137.
-Stehn RA, Richmond ME.1975.Male-induced pregnancy termination in the
prairie vole,Microtus ochrogaster. Science 187: 12111213.
-Stehn RA, Jannett FJ Jr. 1981. Male-induced abortion in various microtine
rodents. Journal of Mammalogy 62: 369372.
-Storey AE. 1994. Pre-implantation pregnancy disruptions in female meadow
voles Microtus pennsylvanicus (Rodentia:Muridae):Male competition or
female mate choice? Ethology 98: 89100.
-Kenney AM,Evans RL, Dewsbury DA. 1977. Postimplantation pregnancy disruption
in Microtus ochrogaster, Microtus pennsylvanicus, and Peromyscus
maniculatus. Journal of Reproduction and Fertility 49: 365367.
-Schwagmeyer PL. 1979. The Bruce effect: An evaluation of male/female advantages.
de la Maza HM,Wolff JO, Lindsey A. 1999. Exposure to strange males does
not cause pregnancy disruption or infanticide in the gray-tailed vole.Behavioral
Ecology and Sociobiology 45: 107113.
in parts from: Wolff, J. O. (2003) Laboratory Studies with
Rodents: Facts or Artifacts? BioScience Forum 421. Vol. 53. No. 4.
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