Bone loss is a physiological cost of reproduction in white-footed mice (Peromyscus leucopus)

Investment in offspring production often requires the mobilization of endogenous resources, a strategy that may negatively impact maternal condition. In mammals, skeletal ossification in growing offspring requires a large investment of calcium by mothers, and bone loss has been described in several species as a means of supporting this demand. Although bone loss can have adverse effects on the mother, its potential role in a reproductive trade-off has not been addressed. Using white-footed mice (Peromyscus leucopus), we tested the effect of dietary calcium availability on maternal skeletal condition during reproduction to assess if calcium availability drives a trade-off between maternal skeletal condition and offspring production. We provided mice with a low-calcium or standard diet and monitored reproductive output along with changes in bone mineral density and bone resorption (via serum concentrations of pyridinoline cross-links) throughout reproduction. Reproductive performance was not impaired by low calcium intake. Reproductive females on the low-calcium diet showed a significant reduction in bone mineral density relative to reproductive females consuming the standard diet and non-reproductive mice consuming the low-calcium diet, but no difference in bone resorptive activity. Our results suggest that when dietary calcium is limited white-footed mice reproduce at the expense of their skeletal condition, and may do so by limiting bone mineral accretion relative to resorption.