GROWTH AND SIZE IN MEADOW VOLES (MICROTUS-PENNSYLVANICUS)

We x-rayed a series of meadow voles (Microtus pennsylvanicus) every 10 days from weaning to 70 days of age to document the occurrence and ontogeny of the relationship between body mass and skeletal size. Males became larger than females in mass and postcranial skeletal measures as they aged but there was no pattern of dimorphism in cranial measures. Both sexes displayed the same patterns of rapid initial growth in mass and skeletal size followed by slower increases later in time. After the slowdown, both mass and skeletal size continued to increase, with mass growing faster. Initially, body mass and skeletal size were associated, but after 30 days postpartum no such association was evident. We concluded that mass is not necessarily the best measure of body size. The different patterns of growth observed might result from voles initially meeting a minimum skeletal size needed to reproduce, then putting any excess investment over and above maintenance and reproduction into soft tissue.