Moshe Jakubowski

Infanticide and caretaking in non-lactating Mus musculus: Influence of genotype, family group and sex

Abstract The involvement of genotype, family group and sex in the regulation of the response to young was studied in non-lactating wild versus laboratory house mice (Mus musculus). Regardless of the sex, naive wild mice typically killed young, in contrast to laboratory mice, which characteristically exhibited parental care. After cohabiting with parents attending their offspring, wild males exhibited paternal behaviour, while the majority of wild virgin females continued to display infanticide. Contrary to the prevailing view, the results indicate that (a) parental behaviour in wild mice does not occur spontaneously, and (b) the domesticated mouse may not always reliably represent the species Mus musculus in behavioural studies.

Incidence of pup killing and parental behavior in virgin female and male rats (Rattus norvegicus): differences between Wistar and Sprague-Dawley stocks.

The responses toward young shown by males and nulliparous females differed substantially between two outbred stocks of laboratory rats. Sprague-Dawley females showed maternal behavior either spontaneously (35% of the naive rats) or through concaveation (92% of the initially neutral virgins). Of the Wistar females, however, only 10% showed maternal behavior spontaneously, and only 29% of the neutral virgins came to behave maternally during 15 days of concaveation. Prepubertal cohabitation with lactating rats did not facilitate maternal responsiveness in adulthood in the Wistar virgin females. Of the Sprague-Dawley males, 50% showed paternal behavior spontaneously, and only 4% killed the young. Among the Wistar males, however, only 4% showed paternal behavior spontaneously, and 76% killed pups. Such profound differences between outbred stocks of rats may be a source of discrepancies between the results of studies dealing with the induction of parental behavior in nonlactating rats.

Transition from pup killing to parental behavior in male and virgin female albino rats

In the first part of this study, the effect of habituation to pups was examined in virgin female and male Sprague-Dawley rats that committed infanticide in a screening test. With repeated exposure to test pups (5-10 days old), the rats ceased to commit infanticide and came to behave parentally. Preexposure to inaccessible pups (confined inside wire-mesh baskets) did not accelerate the rate of disappearance of infanticide during subsequent contact with young, which suggests that pup killing is not a neophobic response to the novelty of young. In the second part of the study, three groups of infanticidal male Wistar rats were mated and tested for their responses towards unrelated pups after different intervals of cohabitation with their mates. The males continued to commit infanticide at the time that their mates were at midpregnancy or 24 hr before parturition, but males that cohabited with their mates till day 9 postpartum no longer attacked the young. Thus, the mother rat, presumably by means of postpartum aggression, renders her mate noninfanticidal, thereby reducing the likelihood of her offspring being harmed when she is away from the nest.

Establishment and maintenance of maternal responsiveness in postpartum Wistar rats

Abstract Maternal responsiveness towards 4–10-day-old pups (retrieving, crouching over and licking of pups) was measured in primiparous Wistar rats over a period of 40 days postpartum in a daily. 30-min test. It was found that maternal responsiveness is gradually established during a critical period lasting up to 48 h after parturition. Extended tactile stimulation by young, presumably on the females ventral surface, was indispensable for the establishment of maternal solicitude and for its subsequent maintenance during the course of lactation. Neither teat stimulation by sucking nor exteroceptive stimuli from pups contributed to the establishment or the maintenance of maternal solicitude. It is suggested that the need for physical access to pups may vary among colonies of laboratory rats according to their respective inherent tendencies to care for young.