Iron mobilization during lactation reduces oxygen stores in a diving mammal

Abstract

The profound impacts that maternal provisioning of finite energy resources has on offspring survival have been extensively studied across mammals. This study shows that in addition to calories, high hemoprotein concentrations in diving mammals necessitates exceptional female-to-pup iron transfer. Numerous indices of iron mobilization (ferritin, serum iron, total-iron-binding-capacity, transferrin saturation) were significantly elevated during lactation in adult female Weddell seals (Leptonychotes weddellii), but not in skip-breeders. Iron was mobilized from endogenous stores for incorporation into the Weddell seal’s milk at concentrations up to 100× higher than terrestrial mammals. Such high rates of iron offload to offspring drew from the female’s own heme stores and led to compromised physiologic dive capacities (hemoglobin, myoglobin, and total body oxygen stores) after weaning their pups, which was further reflected in shorter dive durations. We demonstrate that lactational iron transfer shapes physiologic dive thresholds, identifying a cost of reproduction to a marine mammal.

Pack-ice seals contribute to biological transfers of iron in the Southern Ocean

“…This provides confidence in our model outputs (Table 3 and Online Resource 1). rFe has in contrast never been measured on pinnipeds, but as mammals, adult seals (excluding pregnant and lactating females, see Shero et al (2022)) are expected to defaecate any iron that they do not require to maintain their body homeostasis (Candela et al 1984;Ratnarajah et al 2014). Its small influence on the final output variability was expected, as it is close to one.…”