Development of Thermoregulatory Capability in Weddell Seal Pups

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One of the greatest metabolic costs for endotherms is the energy allocated to thermoregulation. Weddell seals (Leptonychotes weddellii) are the southernmost breeding mammals, and as such are born into one of the most challenging thermal environments on the planet. During their nursing period, Weddell seal pups must develop the capability to survive both on the ice and in the water. Pups also concurrently shift from the use of fur to a reliance on blubber for insulation. This study examined the thermal and energetic costs associated with development and thermoregulation in Weddell seal pups. Metabolic rate (MR) in air was measured longitudinally for 4 pups every 2 weeks, starting at 1 week of age through the transition to independence (7 weeks); MR in water was measured in the same pups beginning at 3 weeks. Additionally, we assessed the molt status of each pup, and estimated body composition (blubber vs. lean mass) based on an elliptical cones model. There was a high degree of individual variability in mass‐specific MR in air in 1 week old pups (5.96–10.87 ml O2 min−1 kg−1), though in general it remained stable or decreased slightly from 1–7 weeks of age. Mass‐specific MR in water declined from 3 weeks to 7 weeks of age for 2 of the 4 pups, and remained stable for 2 pups. The difference between mass‐specific MR in air and in water also decreased from 3 to 7 weeks for 2 pups and remained steady for 2 pups; but by 5 weeks of age the difference between MR in air and in water was marginal for all 4 pups. Timing of the initiation of the molt and molt duration was also variable; two pups had molted patches by 3 weeks of age, and all but 1 pup were fully molted by 7 weeks of age. All pups gained mass from 1 to 5 weeks of age at an average rate of 2.02 ± 0.09 kg day−1 and the proportion of blubber increased from 1–3 weeks (25% to 38% of body mass). Blubber proportion remained steady from 3–5 weeks (38% to 40% of body mass) because pups gained proportionally more lean mass (61% of total mass gained). By 7 weeks, 3 of the 4 pups had weaned and were losing mass. Timing of MR equivalence in air and water did not vary with molt status (amount of lanugo) or with estimated body composition. Overall, these results indicate that Weddell seal pups have developed their thermal capabilities by ~5 weeks of age to protect themselves against increased heat loss in water, independent of the amount of lanugo fur or body composition.Support or Funding InformationThis project was funded by the National Science Foundation, Office of Polar Programs (#1543539).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.