Pregnancy Blocking in Rodents: Adaptive Advantages for Females

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Abstract
Recently inseminated female rodents exposed to strange males or their odors lose developing embryos and return to estrus. This pregnancy blocking phenomenon has been interpreted as a strategy to increase male reproductive success and reduce their chances of caring for unrelated infants. The adaptive significance for females remains unclear. Pregnancy blocking may have actually evolved as a female mechanism to minimize parental investment in offspring which are potentially susceptible to infanticide by the strange male. Data reported for other mammals and 1 sp. of bird [Streptopelia risoria] are reinterpreted from the perspective of female reproductive advantage.