Meeting Abstract

113.1  Tuesday, Jan. 7 10:30  Thermoregulatory strategy shifts with development in harp seal pups (Pagophilus groenlandicus) LIWANAG, HEM*; PEARSON, LE; MARCOS, C; GMUCA, N; HAMMILL, MO; BURNS, JM; Adelphi University; University of Alaska Fairbanks; Adelphi University; Adelphi University; Maurice Lamontagne Institute; University of Alaska Anchorage hliwanag@adelphi.edu

Mammals must balance heat production with heat loss to maintain thermoregulatory homeostasis. Animals born in polar regions face additional challenges because extreme environmental conditions and small body size intensify heat loss. Harp seals (Pagophilus groenlandicus) are born on pack ice, with little blubber and a wettable lanugo coat; twelve days later, weaned pups have a developed blubber layer and begin to molt their pelt. To determine if thermoregulatory capability and strategy change as pups develop, we examined 5 age classes of harp seal from birth to post-molt. We measured insulative capacity through percent blubber, blubber and pelt thermal conductivity, and thermal resistance. We assessed potential for additional heat generation by non-shivering thermogenesis (NST), through uncoupling protein 1 (UCP1) expression and mitochondrial density in brown adipose tissue (BAT). Blubber volume significantly increased with age (P<0.001), but there was no significant difference in blubber conductivity across age classes (P=0.969). Pelt conductivity also did not differ, except in 9-day old pups, which had higher conductivity (P<0.001). Although overall thermal resistance did not differ among ages (P=0.948), the contribution of blubber increased from 17.5±0.03% of resistance in neonates to 75.87±0.01% of resistance after 3 weeks. While BAT of younger pups expressed UCP1, expression and mitochondrial density quickly declined, and the ability to produce heat via NST was lost by weaning. UCP1 expression was negatively correlated with increasing percent blubber across age classes (r²=0.756, P=0.001). Together, these findings suggest additional thermogenesis is no longer necessary when blubber, rather than wettable fur, is the main thermal barrier.