Mammalian Adaptations to Winter

1. Mammalian Adaptations to Winter Life in the Cold Jessica Healy Winter Ecology Spring 2009 From picasaweb.google.com/.../9KWZbkSAd_NQ3ZX-kLmoIA

2. Mammalian Adaptations to Winter • Dealing with cold • Hibernation • How we study hibernation • Future directions

3. Dealing with cold—Animals in general • Avoid it • Migrate • Insulate • Burrows • Hair • Fat • Size • Deal with it • Freeze • Hibernate

4. Response to cold environments: Freeze avoidance vs. Freeze tolerance

5. Dealing with cold—Mammals • Increase insulation • Decrease heat loss • Increase metabolism • Decrease metabolic costs

6. Increase insulation • Fur • Fat • Size • Burrowing

7. Decrease heat loss • Vasoconstriction • Piloerection • Countercurrent exchange

8. Increase metabolism • Physiological Thermogenesis: • Basal Metabolic Rate (BMR) • Produces heat and ATP • Shivering thermogenesis • Non-synchronous contraction of skeletal muscle • Non-shivering thermogenesis (NST) • Brown adipose tissue (BAT) • Metabolismmax = BMR + NST + shivering

9. Temperature and metabolic rate Figure 8.33 from Environmental Physiology of Animals (2nd edition) by Pat Willmer, Graham Stone, & Ian Johnston (2005).

10. Decrease metabolism—torpor and hibernation

11. Torpor and Hibernation • Torpor=naturally occurring drop in Tb (body temp) with resulting drop in metabolism, circulation, and respiratory rates • Who uses torpor? • Birds, reptiles, amphibians, mammals • How is torpor different from hypothermia? • Core temperature defended at low level in torpor • Time taken to arouse • Euthermia=normal warm Tb

12. Torpor and Hibernation (cont) • Estivation=torpor bouts in summer • Hibernation=multi-day torpor bouts in winter • Endothermy NOT abandoned—regulate temp at lower level • Which animals hibernate? • Carnivores • Rodents • Insectivores • Monotremes • Marsupials • Some ectotherms

13. Hibernation • How developed? • Ancestral condition • Evolved separately in birds and mammals • Why do only some members of each group hibernate? • Size • Resource availability • ‘True’ hibernation vs. ‘winter lethargy’ • True hibernators are smaller, drop Tb to close to ambient, bouts last several days • Winter lethargy (bears, carnivores)—temp drops a few degrees, bouts last weeks-months

14. The Hibernation Cycle:

15. Hibernation (cont) • A typical torpor bout (marmot): • Animal drops Tb to near Ta, slows metabolism (2-6 hours) • Respiration, heart, metabolic rates drop • Synapses separate in brain—brain dead! • Animal remains at low tissue temp (6-8 days) • Metabolic process occur at very low levels • Animal returns to euthermic temperature (1-2 hours) • Synapses re-grow, metabolic & cardiovascular rates speed up, animal becomes active

16. Typical hibernation season

17. Why study hibernation? • Implications for obesity research • Surgery/transplants • Understanding extreme physiology • Space travel • Indicator of climate change

18. Obesity and hibernation • Obesity=excessive accumulation of body fat • Generally considered pathogenic • Diabetes, atherosclerosis, osteoarthritis • Hibernating animals become fat without associated pathologies • How?? • Natural selection • Hormone pathway blocking • Time span/seasonality of obesity

19. Model Animals • Golden-mantled ground squirrels (GMGS) • Spermophilus lateralis • Summer weight 150 g • Winter weight 350 g • Yellow-bellied marmots • Marmota flaviventris • Summer weight 2 kilos • Winter weight 5 kilos • Woodchucks • Marmota monax • Summer weight 2 kilos • Winter weight 5 kilos

20. How do we study hibernators? • Only above-ground for 4-5 months • Field observations • Diet, behavior, fecundity • Field experiments • Implant data loggers for Tb, activity • Lab observations • How behavior/torpor patterns differ in lab • Lab experiments • Hormone injections, temperature manipulations

21. FieldObservation Pictures by G. F. Florant

22. How do we study hibernators? • Only above-ground for 4-5 months • Field observations • Diet, behavior, fecundity • Field experiments • Implant data loggers for Tb, activity • Lab observations • How behavior/torpor patterns differ in lab • Lab experiments • Hormone injections, temperature manipulations

23. Field Experiments Pictures by G. F. Florant

24. Torpor patterns vary with latitude Maine Latitude/Longitude: 43°42’N / 70°14’W Elevation: 10 m Avg. Ambient Temp.: -5.9 °C Avg. Burrow Temp.: 4.6 °C Pennsylvania Latitude/Longitude: 40°22’N / 75°22’W Elevation: 85 m Avg. Ambient Temp.: 3.2 °C Avg. Burrow Temp.: 7.7 °C South Carolina Latitude/Longitude: 34°40’N / 82°50’W Elevation: 45 m Avg. Ambient Temp.: 9.8 °C Avg. Burrow Temp.: 12.8 °C *Data from Stam Zervanos et al 2008

25. Torpor patterns vary with latitude Maine Pennsylvania South Carolina *Data from Stam Zervanos et al 2008

26. How do we study hibernators? • Only above-ground for 4-5 months • Field observations • Diet, behavior, fecundity • Field experiments • Implant data loggers for Tb, activity • Lab observations • How behavior/torpor patterns differ in lab • Lab experiments • Hormone injections, temperature manipulations

27. Lab work

28. What can we measure? • Body temperature (implanted data loggers, temp tracking radio collars) • Hormone levels (factors in obesity, food intake) • Dietary choices (energy levels, fatty acids for membrane fluidity) • Behavior (constrained by food intake, dietary choices)

29. Lab activity levels

31. Future directions • Little is known about many aspects of hibernation • Periodic arousals—why? • Control mechanism for suppressing metabolism—how? • Hibernation dynamics in field—hard to get real-time data • How can this knowledge benefit humans? • Implications for climate change?

32. Questions?