Inbreeding-based bias in parental responsiveness to litters of oldfield mice

This study investigated variation in parental behavior in oldfield mice (Peromyscus polionotus). Specifically, I examined the possibility that parental behavior and probability of litter loss may differ depending on whether parents are related to one another and, therefore, whether offspring are inbred. When parents are related, they share more genes with their offspring and so may be predicted to invest more in inbred offspring if these offspring do not inherently have a greater risk of juvenile mortality. Survival of inbred pups did not differ from survival of outbred pups, and females tended to exhibit a preference, in the form of enhanced parental care, for inbred litters. Males did not display any consistent preferences. Inbred litters were left unattended more often during the immediate post-partum period than were outbred litters, but this inconsistent finding appeared to have a smaller effect than the overall improved maternal care provided to inbred litters. Females thus appeared to modulate their behavior to a greater degree than did males depending on characteristics of the litter. Patterns of litter loss indicated that complete death of litters was independent of litter inbreeding, whereas loss of selected pups in a litter occurred significantly more often when litters were inbred. Complete and partial loss of litters may be functionally different behaviors that are triggered by different cues. Received: 20 September 1996 / Accepted after revision: 28 April 1997