Sire Behaviour in the Context of Novel Males: The Sire Protection Effect

Abstract

Female mammals are known to exhibit pregnancy failure when exposed to various stimuli during the implantation phase of pregnancy. When newly inseminated female mice are exposed to novel males in the absence of the sire, implantation is disrupted. This phenomenon is known as the Bruce effect. When females are exposed to novel males in the presence of the sire, pregnancy failure does not occur. This latter effect has been referred to as the sire protection effect. In these studies we examine the nature of female and sire behaviour in the context of novel males. Female interactions with novel males significantly decrease in the presence of the sire. This reduction in female-novel male interaction in seen irrespective of whether sires are free or confined within the female's cage. Novel-male exposed females exhibit pregnancy failure and this pregnancy block is removed when either free of corral-confined sires remain present in the cage. Finally, sires are highly motivated to engage in aggressive conflicts with novel males both in the presence and absence of the pregnant female. Sires were observed to behave aggressively towards novel males through a wire-mesh grid and in this context were able to inflict severe wounding upon novel males through the wire-mesh partition. In a direct exposure paradigm, sires were also witnessed to exhibit this aggression and were found to initiate and win all conflicts with novel males. The sire protection affect is likely to involve a complex of both pheromonal and behavioural cues. Sire aggression towards novel males, pheromonal communication and limited behavioural interaction between the sire and the female, and reduced femalenovel male interaction are all likely components of the effect.