Meeting Abstract
In marine mammals, there is profound energetic transfer from female to pup during lactation, when capital breeding females can lose >30% of their body mass and pups triple in size. In addition to fat and calories, milk also transfers many essential nutrients. For deep divers that rely on large tissue O2 stores to support foraging efforts, maternal transfer of iron is critical to neonatal heme development. However, iron transfer may pose additional reproductive costs to the female if her endogenous reserves are depleted, compromising dive capacity. To assess this potential cost, we handled reproductive Weddell seals (Leptonychotes weddellii; n=143; at start and end of nursing, and postweaning) and compared their iron stores to those of 148 non-lactating females. During lactation, females’ circulating iron levels were significantly higher than in non-lactating seals (P<0.001; 266±10 vs 122±7µg/dL), and iron binding proteins were also elevated (Ps<0.001 transferrin saturation: 64±2 vs 44±2%; ferritin concentration: 191±18 vs 96±12 ng/mL), suggesting iron was mobilized from endogenous stores. Serum iron levels were positively correlated with milk iron content (P<0.001), and Weddell seal milk contained 150-fold and 5-fold more iron than milk from other terrestrial and marine mammals, respectively. Mobilizing endogenous iron to milk appears to deplete reserves, and adult female hemoglobin and myoglobin levels declined soon after weaning, reducing total body oxygen stores and aerobic dive capacities (pre-weaning: 130±2mLO2, post: 107±2mLO2 lean kg-1, P<0.001). This study shows that iron transferred from mother to pup during lactation reflects a previously unexplored cost to the capital breeding strategy.
