Temperature Relationships

1. Temperature Relationships

2. What do amphibians and reptiles have in common? • Evolutionarily speaking, “herpetiles” are a somewhat unnatural grouping but ectothermy: • is a reliance on solar radiation to raise body temperatures to a functional level • provides an important link • In contrast, endotherms (e.g. birds and mammals) regulate body temperature by metabolizing the food they eat

3. Ectothermy vs. Endothermy • Ectothermy: Greek ‘Ectos’ = outside, ‘Thermos’ = warm/heat • Endothermy: Greek ‘Endo’ = within, ‘Thermos’ = warm/heat

4. Why does body temperature matter? • Biochemical reactions allow organisms to function • Rates of depend strongly on temperature • Temperature also affects the rate of travel of nerve impulses and rate of muscle contractions • Regulation of body temperature is essential for organisms to function

5. Why does body temperature matter? Effects of Temperature on Garter Snake Activity

6. Map turtles… http://www.bioone.org/doi/pdf/10.1670/07-1881.1

7. Let’s not use “cold-blooded”!

8. Ectothermy vs. Endothermy • Ectotherms are FAR more energy efficient • A lizard uses ~ 3% as much energy in a day as a similar sized mammal in the same habitat • They are able to convert a greater percentage of the energy they consume into body tissue (50% compared to 2% for endotherms)

9. Efficiency of Biomass Conversion

10. Implications of Ectothermy • When food is scarce, ectotherms can go into torpor • Organism is out of sight and virtually inactive for sometimes months or years • Allows for exploitation of episodic food resources

11. Implications of Ectothermy • Ectotherms are often extremely productive (prolific) • Can produce lots of biomass with little energy input • Thus, they can produce lots of offspring

12. Ectothermy vs. Endothermy On the other hand….. • It is difficult for ectotherms to maintain their body temperature in an ideal range in cold climates • This limits their distribution in space and time • Many species are only active in warm seasons • At risk of predation during periods of inactivity

13. Ectothermy vs. Endothermy Body Size Interactions…… • Being a small endotherm is energetically very expensive • Being a small ectotherm is relatively efficient • Most amphibians and reptiles are small in comparison to birds and mammals

14. It is simply not energetically feasible to be a small (< 10 g) bird or mammal! Size Matters…… • Surface to volume ratio decreases with increased size • Surface Area = 6 x length2 • Volume = length3 • Heat gain and loss occurs more slowly in larger individuals SA = 24 V = 8 3:1 SA = 6V = 16:1

15. Resting metabolic rate as a function of body size

16. Ectothermy vs. Endothermy Body Size implications… Body Mass Mammals Salamanders Lizards

17. Ectothermy and Body Size • Allows ectotherms to exploit "small body size" niches that are unavailable to larger endotherms. • “Small body size" niche dimensions include • small habitat patches (e.g., cups formed by tropical bromeliads, cracks in bedrock) • small food items • small shelters (e.g., cracks in bark)

18. Small size: Rapid control over body temperature by shuttling between different thermal regimes Large size: some advantage -- Inertial homeothermy.

19. Ectothermy has important implications for how energy flows in ecosystems

20. One example… • Found about 10,000 redback salamanders/ha • Each weigh about 1 g, so there’s about 10 kg salamanders/ha • There are some 180 billion RBS in NYS! • Energy conversion rate of 60% • (Burton and Likens, 1975, Ecology 56:1068-1080)

21. Redback salamanders • Regulate decomposition rates of the leaf litter by limiting invertebrate populations • Major food item for predators “above” them in the food chain • Essentially "repackage" energy from small prey items into forms that larger species (including endotherms) can exploit • Major conduit of energy and minerals • Without ectotherms, the abundance and diversity of endotherms would be much lower! • Play role in global carbon cycles.

22. Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Infrared Gain Conduction Gaining and losing heat

23. Terminology • Thermal performance breadth (activity temperature range) - The temperature range over which an individual is active • Critical thermal minima and maxima (CTmin, CTmax) - Lethal higher and lower temperatures • Optimal temperature - The temperature over which performance of some biochemical or behavioral task is maximized. Different tasks may have different optima.

24. Sevilleta box turtles project

26. Lizards Radiating Heat

28. Absorbing Solar Radiation Qabs = S ·A · vfs · a Rate of absorption of solar energy depends on: • The intensity of the radiation (S) • Surface area of the animal (A) • Proportion of the animal’s surface that is exposed to the radiation (vfs) • Absorptivity, proportion of the energy that is absorbed rather than reflected (a) Herps have substantial control over the amount of solar radiation they absorb

29. Absorbing Solar Radiation • Move between sun and shade • Change the amount of surface area exposed to the sun • Change orientation to the sun • Change color (albedo) to change absorptivity • Concentrate pigments in melanophores to expose reflective pigments and cast off light. • Disperse melanin to absorb light

31. Basking • Common in reptiles and amphibians • Involves relocation and postural adjustment to maximize surface area exposed to sun

32. More on basking… • Sun patches critical, especially in low light environments (forests, wetlands). • Egg laying • Varies by life stage • Recent metamorphs of many nocturnal species are very diurnal • Diurnal activity corresponds to higher growth rates and rates of fat storage • Gestation in adult females

33. Basking to purge diseases? • Batrachochytrium dendrobatidis (Bd) is a fungus that can induce chytridiomycosis • Bd cannot live above 30oC

34. Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation InfraredLoss Infrared Gain Conduction Gaining and losing heat

35. Absorbing Infrared Radiation • Heat is constantly exchanged between an animal and its environment in the form of infrared radiation • Heat is transferred from the warmer surface to the cooler surface • The amount of heat an animal gains from infrared radiation depends partly on how easily a surface radiates and absorbs the infrared energy

36. Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Infrared Gain Conduction Gaining and losing heat

37. Producing Metabolic Heat • Some chemical energy is lost as heat during metabolic processes • A few reptiles, especially large species, use metabolic heat production (endothermy)

38. Producing Metabolic Heat • E.g. The leatherback turtle (Dermochelys coriacea) • In leatherbacks, heat is generated through muscular activity • Retained by insulative thick, oil-filled skin • Can maintain body temperatures of 25oC in 8oC seawater and range into cold northern seas.

39. Producing Metabolic Heat • E.g. Pythons • Females use the heat produced by muscle contractions to incubate their eggs • Metabolic rate during brooding 20 x that of non-brooding females • Eggs are maintained at ~30° C

41. Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Infrared Gain Conduction Gaining and losing heat

42. Convection • Heat exchange between a solid and a fluid medium (air or water) • Involves differing amount of contact with fluid flows, especially, wind Side blotched lizard, Uta stansburiana

43. Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Infrared Gain Conduction Gaining and losing heat

44. Conduction • Exchange from solid to solid • Managed mainly through posture shifts that change the degree of body contact with substrate • Conduction is especially important for fossorial species • Nocturnal species

45. Direct solar radiation Reflected solar radiation Convection Metabolic Heat Evaporation Infrared Loss Infrared Gain Conduction Gaining and losing heat

46. Evaporative Cooling • Water passed across skin, vaporizes on surface • Conversion of water from liquid to gaseous phase involves a large loss of heat. • Last step is convection of water vapor. • E.g., in reptiles: panting, salivation, urination on limbs and body.

47. Evaporative Cooling: A major issue for amphibians • Skin is so permeable that high water loss is continuous. • Limits the thermal regulatory ability of amphibians. • Only a few have any physiological control over evaporative heat loss, e.g., some arboreal tree frogs (e.g., Phylomedusa spp).

48. Evaporative Cooling: E.g. Green frogs (Rana clamitans) and Bull frogs (Rana catesbeiana)

49. Evaporative Cooling: Phyllomedusa spp. • Secretes wax that seals itself up – when very high temperatures are achieved, then wax melts and evaporative cooling ensues

50. Reptile Skin and thermoregulation • Highly impermeable skin, permits direct exposure to sunlight without excessive water loss • Hence temperature control is much more common in reptiles