Maternal-care behavior and life-history traits in house mice (Mus domesticus) artificially selected for high voluntary wheel-running activity

To test the hypothesis that selective breeding for high voluntary wheel running negatively affects maternal performance in house mice, we observed maternal behavior and compared litter size and mass, in replicate lines of selected (N=4) and control (N=4) mice from generations 20 and 21 of an artificial selection experiment. At generation 21, selected-line females ran 2.8-times more revolutions per day than females from random-bred control lines, when tested at approximately 6 weeks of age as part of the normal selection protocol. After giving birth, dams from selected and control lines exhibited similar frequencies of maternal behaviors and also spent similar amounts of time in general locomotor activity at litter ages of both 9 and 16 days. Dams from selected lines also performed equally well as controls in repeated pup-retrieval trials. At first parturition, selected-line dams averaged 2.4 g smaller in body mass as compared with dams from the control lines; however, neither litter size nor litter mass at birth (generation 20) or at weaning (generation 21) differed significantly between selected and control lines. We conclude that, at least under the husbandry conditions employed, maternal behavior and reproductive output at first parturition are genetically independent of wheel-running behavior.