Fig. 1. Iron mobilization increased during the austral summer in lactating post-partum females, but not skip-breeders.

Mean ± SE (a) Plasma ferritin (red points), and serum iron (black points) and total iron binding capacities (TIBC; blue points) increased during lactation, whereas (b) unsaturated iron binding capacities (UIBC) did not vary among reproductive classes. c This resulted in significantly higher transferrin saturation levels (percentage of sites bound with iron) during lactation in post-partum females as compared with skip-breeders. Red points denote transferrin saturation levels that would indicate iron overload in humans (>45%); blue points show transferrin saturation levels within the normal range for other mammals; note that points are jittered on the x-axis. In boxplots, boxes encompass the interquartile range, the center line denotes the median, whiskers encompass range of values, and points above or below the whiskers are greater/less than 1.5-times the interquartile range. d Plasma ceruloplasmin declined during lactation in female Weddell seals. Statistical significance was detected using Linear Mixed-Effect models and post-hoc comparisons with Bonferroni correction; Different letters = significant difference between reproductive classes. Serum iron, TIBC, UIBC, Tf-Sat - Skip-breeder n: Early summer = 60, Late summer = 79; Post-Partum n: Beginning Lactation (7 dpp) = 17, End Lactation (35 dpp) = 61, Post-weaning (95 dpp) = 60. Ferritin and Ceruloplasmin - Skip-breeder n: Early summer = 16, Late summer = 27; Post-Partum n: Beginning Lactation (7 dpp) = 10, End Lactation (35 dpp) = 16, Post-weaning (95 dpp) = 17. Photo credit: Michelle Shero.