title: To each its own: Thermoregulatory strategy varies among neonatal polar phocids.
abstract: Cold environmental conditions and small body size promote heat loss and may create thermoregulatory challenges for marine mammals born in polar regions. However, among polar-born phocid seal species there are variations in physical attributes and environmental conditions at birth, allowing for an interesting contrast in thermoregulatory strategy. We compared thermoregulatory strategies through morphometrics, sculp attributes (conductivity and resistance), nonshivering thermogenesis (NST via uncoupling protein 1; UCP1), and muscle thermogenesis (via enzyme activity) in neonatal harp (Pagophilus groenlandicus), hooded (Cystophora cristata), and Weddell seals (Leptonychotes weddellii). Harp seals are the smallest at birth (9.8±0.7 kg), rely on lanugo (82.49±3.70% of thermal resistance), and are capable of NST through expression of UCP1 in brown adipose tissue (BAT). In contrast, hooded seal neonates (26.8±1.3 kg) have 2.06±0.23 cm of blubber, accounting for 38.19±6.07% of their thermal resistance. They are not capable of NST, as UCP1 is not expressed. The large Weddell seal neonates (31.5±4.9 kg) rely on lanugo (89.85±1.25% of thermal resistance) like harp seals, but no evidence of BAT was found. Muscle enzyme activity was highest in Weddell seal neonates, suggesting that they rely primarily on muscle thermogenesis. Similar total thermal resistance, combined with marked differences in thermogenic capacity of NST and ST among species, strongly supports that thermoregulatory strategy in neonatal phocids is more closely tied to pups' surface area to volume ratio (SA:V) and potential for early water immersion rather than mass and ambient environmental conditions.
authors.affiliation: School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 905N. Koyukuk Dr., Fairbanks, AK 99775-7220, USA; Department of Biology, University of Alaska Anchorage, 3101 Science Cir., Anchorage, AK 99508, USA. Electronic address: lepearson@alaska.edu.
authors.forename: Linnea E
authors.initials: LE
authors.lastname: Pearson
authors.affiliation: Department of Biology, Adelphi University, 1 South Ave., Garden City, NY 11530, USA.
authors.forename: Heather E M
authors.initials: HE
authors.lastname: Liwanag
authors.affiliation: Department of Fisheries and Oceans, Maurice Lamontagne Institute, 850 route de la Mer, Mont-Joli, Quebec H5H 3Z4, Canada.
authors.forename: Mike O
authors.initials: MO
authors.lastname: Hammill
authors.affiliation: Department of Biology, University of Alaska Anchorage, 3101 Science Cir., Anchorage, AK 99508, USA.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Burns
mesh_terms: D002001:Adipose Tissue, Brown / Q000254:growth & development / Q000502:physiology; D050154:Adiposity; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development / Q000502:physiology*; D000864:Antarctic Regions; D001110:Arctic Regions; D001724:Birth Weight; D001833:Body Temperature Regulation; D002170:Canada; D005260:Female; D006116:Greenland; D006197:Hair / Q000254:growth & development / Q000502:physiology; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D024101:Mitochondrial Proteins / Q000378:metabolism; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000201:enzymology / Q000254:growth & development / Q000502:physiology; D046048:Seals, Earless / Q000254:growth & development / Q000502:physiology*; D012867:Skin / Q000254:growth & development; D012879:Skin Physiological Phenomena; D013045:Species Specificity; D050151:Subcutaneous Fat / Q000254:growth & development / Q000502:physiology; D013814:Thermal Conductivity; D000071256:Uncoupling Protein 1
chemical_list: D007473:Ion Channels; D024101:Mitochondrial Proteins; D000071256:Uncoupling Protein 1
keywords: Blubber; Harp seal; Hooded seal; Lanugo; Nonshivering thermogenesis; Thermal conductivity; Thermoregulation; Weddell seal