Body weight, litter size, and energetics of reproduction in Clethrionomys gapperi and Microtus pennsylvanicus

A forest vole, Clethrionomys gapperi, and a field vole, Microtus pennsylvanicus, were examined for differences in a number of reproductive traits, including the energy required to raise a litter. Average postpartum weight, litter weight, and neonate weight of C. gapperi were significantly less than those of M. pennsylvanicus. Although C. gapperi had a significantly larger litter size than M. pennsylvanicus, the latter species used more energy to raise a litter than C. gapperi. Only one of three measures of physiological reproductive effort showed a significant difference between species. We conclude that there is no clear pattern between reproductive traits and habitat. Many traits appear to vary with body weight.