THE EFFECT OF INTRAUTERINE POSITION ON THE SURVIVAL, REPRODUCTION AND HOME RANGE SIZE OF FEMALE HOUSE MICE (MUS-MUSCULUS)

In laboratory studies using albino house mice, a female's prior intrauterine position can affect many postnatal physiological, morphological and behavioral characteristics. Females flanked by males in utero (2 M females) exhibit more aggressive dominance than females flanked by females (0 M females). Thus, wild 2 M females may be most successful during peak population densities when their aggressive nature would allow them to displace other females from limited resources. 2 M and 0 M females and males delivered by cesarean section were individually marked and released as young adults on two occasions onto a "highway island" (the area enclosed by exit and entrance ramps at an interchange) to determine whether 2 M females have a competitive advantage over 0 M females in the field. Males were included to create realistic population structure; their intrauterine position was not a treatment. Feeding stations afforded individuals an opportunity to exhibit their dominance by maintaining home-ranges at or near the stations. The populations were monitored by periodic live-trapping and reproductive success was determined using field body weights and by post-mortem examination for uterine implantation scars. Survival and capture rates were estimated, using a modified Jolly-Seber mark-recapture program, for each of four intervals between trapping occasions over the course of 7 weeks. There were no overall differences in survivorship between 2 M and 0 M females, neither type of female was caught more frequently at feeding stations and they did not differ in measures of reproductive success. However, 2 M females had significantly larger home-range sizes than 0 M females and thus space use may be a trait "masculinized" by prior intrauterine position. Although there are a number of life-history characteristics that differ between 0 M and 2 M females in the laboratory that we did not test specifically in the field, our findings and other features of wild house mouse biology suggest that prior intrauterine position does not have a strong effect on survival and reproduction in the wild.