Differential Effects of Inbreeding at Juvenile and Adult Life-History Stages in Peromyscus polionotus

Abstract

Inbreeding depression traditionally has been measured at early life-history stages, such as neonatal or juvenile viability or deficits in growth and development. I investigated additional fitness components by evaluating impact of inbreeding on reproductive success of adult females in a captive colony of oldfield mice (Peromyscus polionotus subgriseus and P. p. rhoadsi). By first conducting analyses on only inbreeding of litters (i.e., relatedness of parents) and then adding maternal effects (mother's inbreeding coefficient independent of parental relatedness, parity, and maternal inactivity), I illustrated effect of inbreeding on life-history characters that were manifested in adulthood. Young in inbred litters (f > 0.1) tended to be smaller than young in outbred litters, but inbred litters did not exhibit any decrements in survival probability. Number of young raised to weaning from inbred and outbred litters did not differ. Inbred females (inbreeding coefficient f > 0.1) reared significantly fewer young than did outbred females (f < 0.1) (independent of whether parents were related and therefore independent of whether young themselves were inbred). Differences between the two subspecies were found for a number of fitness traits. These differences are attributed to chance differences in genetic makeup of founder stocks (founder effect). Examining inbreeding effects only at a single life-history stage (i.e., during the juvenile period) and only on a single fitness trait (juvenile viability) may result in serious underestimation of the extent of inbreeding depression.