Graduate Research Course
Polar Bear Biophysics
From ice-edge hunting to hibernation biochemistry — the extreme physiology of Ursus maritimus and its Arctic brown-bear relatives under a retreating cryosphere.
About This Course
The polar bear (Ursus maritimus) diverged from the brown bear (U. arctos) less than 500 000 years ago — an eye-blink in mammalian time — yet its physiology, ecology and molecular biology are transformed. A 500-kg Svalbard male stalks ringed seals from ice floes, swims 600 km across open water, fasts through hibernation-like “walking hibernation” states, and catabolises pure fat through a genome enriched in lipid-handling adaptations at APOB, LYPLA1, and the APOB/LDLR axis.
Cross-links: Climate & Biodiversity M9 Polar Regions,Polar Penguins,Polar Seals, and Cetacean Biophysics for the marine-mammal counterparts.
Key Equations
Heat Conduction Through Blubber
\( \dot{Q} = -kA\,\frac{dT}{dx} \)
Ursus Fast Metabolism
\( P_{fast} = P_{BMR}\,e^{-\tau/T_{fast}} \)
Swimming Drag
\( F_d = \tfrac12 \rho C_d A v^2 \)
Urea Recycling Efficiency
\( \eta_{urea} = \frac{\text{urea}_{re}}{\text{urea}_{prod}} \approx 0.95 \)
Nine Modules
M0
Ursid Evolution & Phylogenomics
Ursidae origins, Ursus maritimus split from Ursus arctos <500 kyr ago (Cahill 2013), genomic adaptations to Arctic, fossil evidence.
M1
Arctic Ice Ecology & Hunting
Sea-ice seal ambush, breathing-hole stalking, still-hunting energetics, scent detection across 30 km, GPS telemetry observations.
M2
Fat Metabolism & Insulation
Hollow-shaft guard hair optics (NOT fiber-optics myth debunked), 11-cm blubber, omega-3-enriched fat catabolism, brown adipose absence.
M3
Hibernation Biochemistry
Urea recycling under zero intake, bone-density preservation, Q10 depression, PTT-1 activation, ketogenesis — polar bears only partially hibernate.
M4
Reproduction & Denning
Delayed implantation, 8-month gestation, maternal den thermoregulation, 0.6 kg neonates, cub development, milk composition.
M5
Swimming & Aquatic Foraging
Long-distance swims >500 km (Durner 2011), drag coefficient, aquatic metabolism, newborn cub drowning risk, ringed-seal pursuit swimming.
M6
Climate Change & Bears
Sea-ice-dependent foraging time, Hudson Bay body-condition decline, Stirling & Parkinson 2006 trajectories, cross-links climate-biodiversity M9.
M7
Brown Bear Arctic Variants
Kamchatka (600 kg), Kodiak (680 kg), grizzly salmon runs, hybridization with polar bear (Pizzly/Grolar bears), metabolic contrast.
M8
Conservation & Indigenous Knowledge
Inuit knowledge integration, 1973 Polar Bear Range States Agreement, human-bear conflict as sea-ice retreats, PBSG population estimates.