The proposed research will determine the effects of environmental and life history constraints upon reproduction in common marmosets (Callithrix jacchus). Specific Aim 1 will define the relation between maternal condition and reproductive investment through energy restrictions during gestation or lactation. Based on our preliminary findings, we expect to generate intrauterine growth retardation with minimal change in maternal condition -that is, mothers will sacrifice fetal growth to retain maternal state. We will also be testing the hypothesis that "poor" mothering in multiparous females is the results of "poor" infants (i.e. infants that are small or have an atypical behavioral repertoire). Energy-restriction in the post-partum period is expected to result in more dilute milk and earlier weaning. Specific Aim 2 will define normal calcium metabolism during lactation and determine the effects of calcium restriction on calcium metabolism, milk intake, lactation and bone health in marmosets. This study will indicate whether marmosets might be a useful model for the study of maternal bone health in women, particularly relative to calcium restriction. Specific Aim 3 will define the relation between maternal age, fertility, and survival using a large demographic database. Such information can be used to better define long-term captive propagation. The results will also be useful for defining marmosets as models of life history effects on reproduction and maternal health.