1. Thermoregulation in lizards Dirk Bauwens

2. Thermoregulation n What? n Why? n How should we study it? n Examples studies n Mechanisms? n Interactions other activities

3. Thermoregulation what?  definition

4. target range

6. Definition thermoregulation: Proces by which organisms attempt to maintain their body temperature (T b ):  within a specific target range  divergent from the environmental temperatures  by physiological and/or behavioural adjustments

7. Thermoregulation why?

8. Thermal sensitivity: The rate of biological processes is temperature dependent T opt TPB 80

9. sprint speed catching rate handling rate gut-passage rate energy- intake body mass change T opt TPB 80 Thermal optima in Lacerta vivipara source: Van Damme et al. 1991 (Funct. Ecol. 5: 507- 517)

10. Thermoregulation How to study it?

11. Definition thermoregulation: Proces by which organisms attempt to maintain their body temperature (T b ):  within a specific target range  divergent from the environmental temperatures  by physiological and/or behavioural adjustments

12. Study thermoregulation Requires information on: T b s active lizards Target range (T sel ) Environmental temperatures Mechanisms: behaviour / physiology

13. Study thermoregulation n Body temperatures (T b s) maintained during activity  T b s = final result of regulatory proces  How measure?  “grab and jab”  telemetry  Obtain measurements at different times and places!

14. Study thermoregulation n Target range for T b s  T b s in “ideal” conditions for regulation  Reflect T opt  How measure?  In thermogradient  T sel : upper- and lower limits (80 of 95%) of T b s maintained

15. Study thermoregulation n Environmental temperatures  Quantification of heat exchange between organisms and their environment

16. Heat exchange with environment

17. How to measure environmental temperatures?  Analytical model:  Measure relevant traits of lizards (size, surface area, reflectance skin,...)  Micro-meteo measurements (radiation, wind, T° air, T° substrate, …) in various microhabitats, at different times!  Solve "energy balance equation"

18. Q a + M - E b =  T b - + 273) 4 + H(T b -T a - ) M- E b K K Q a = a s A s S + a s A s s + a s A g r (S + s) + a t (A g R g + A s R a ) H = 3.49 (V/D) O.5 M- E b = 0.096 e Tb/10 - 0.298 e 0.0586Tb Energy Balance Equation

19. How to measure environmental temperatures?  Analytical model: complex & expensive  “Physical” models:  Objects that mimic heat exchange between organisms and environment  e.g. dead lizards, copper models, copper tubes, cans…  “T b ” of model = T e (“operative environmental temperature”)  T b of non thermoregulating organism  (Relatively) easy & cheap

22. How to measure environmental temperatures?  “Physical” models:  “T b ” of model = T e (“operative environmental temperature”)  T e  T b of non-thermoregulating organism  (Relatively) easy & cheap  Large numbers can be used to measure in different microhabitats and times

24. Study thermoregulation  T b s active lizards  Target range: T sel  Environmental temperatures: T e  Behavioural observations (thermo- regulation, social, foraging, …)  Continuous observations (1 lizard – 10 min)  “Scan sampling” (n lizards – 1 sec)

25. Thermoregulation in lizards –Sunny days –Variation during course of day Examples studies

26. Podarcis sicula Podarcis muralis European lizards (Lacertidae)

27. Islas Columbretes (Spain) Palagruža (Croatia)

29. Agama atra (South-Africa)

30. Studies thermoregulation How “well” do lizards thermoregulate? –Similarity of T b s with target range (T sel ): “accuracy” thermoregulation –Deviation of T b s from operative temperatures (T e s): “effectiveness” thermoregulation

31. Podarcis atrata - Body temperatures 102030405060 T sel

32. Podarcis atrata - Operative temperatures 102030405060 0 2 4 6 8 T e Temperature (°C) Percentage of Observations

34. 730900103012001330150016301800 20 30 40 50 60 Hour T sel Temperature (°C) Podarcis atrata - Columbretes

35. Podarcis sicula - Palagruža

36. Agama atra – Jonkershoek (ZA)

37. How “well” do lizards regulate T b ? –T b s almost always within T sel : high “accuracy” of thermoregulation –T b s deviate considerably from T e s: high “effectiveness” of thermoregulation

38. How do lizards regulate their T b ? What “mechanisms” are used? – Ectotherms: physiology unimportant – Behavioural thermoregulation: Restriction of activity times Postures & orientation Selection thermally “suitable” microhabitats

39. Behavioural thermoregulation  To what extent does thermoregulation determine lizard behaviour?  Recall the copper models: T e  T b of non-thermoregulating lizard  At times / places with T e  T sel lizards can easily attain T b  T sel  Let’s look at distributions of T e provided by the copper models

40. Suitability of habitat / time: % models with T e  T sel too cold too warm “ideal”

41. Behavioural thermoregulation  To what extent does thermoregulation determine lizard behaviour?  At times / places with T e  T sel lizards can easily attain T b  T sel  If thermoregulation dictates behaviour, lizards should restrict actvity to times / places where a high % of T e  T sel (“only thermoregulation” hypothesis)

42. Behavioural thermoregulation Main “mechanisms”:  Restriction of activity times  Postures & orientation  Selection thermally “suitable” microhabitats

43. Restriction of activity times  Prediction: active only when heat loads permit to attain T b s  T sel –Seasonal activity (hibernation; aestivation) –Diurnal vs. nocturnal activity –Can we predict daily activity times? – Activity restricted to times when minimal fraction of T e s  T sel

44. Prediction activity times

45. Vaalputs, Karoo Desert (South-Africa)

46. Cordylus polyzonus

47. Cordylus polyzonus – Vaalputs (mid summer)

48. Cordylus polyzonus - Vaalputs (mid-summer)

49. Prediction activity times n Overall good agreement between observed and predicted n Major discrepancies in early morning n Why differences? –Predictions assume “only thermoregulation” and lizards also do other things (forage, social interactions, …) –Lizards avoid T b s > T sel (overheating)

50. Postures & orientation n Usage of postures & adjustment of orientation n Modify the rate of heat exchange with environment n Increase when T e T sel

51. Basking posture  Increase heating rate  Prediction: more often when T e < T sel

52. Podarcis sicula – Palagruža ( 1 point = 1 hour period)

54. Cordylus polyzonus – orientations & postures “perpendicular” Maximize body surface exposed to sun “transverse”“parallel” Minimize body surface exposed to sun Flanks exposed to sun

56. Cordylus polyzonus - Orientation to Sun r = 0.84, P < 0.001

57. Selection microhabitats  Selection of thermally suitable micro-habitats  “Only thermoregulation”: hour-to-hour variation in thermal suitability (and availability) of microhabitats determines their usage  T e measurements  predictions about microclimate usage at different times

58. Podarcis sicula - microhabitat use

59. P. sicula - predicted and observed microhabitat use r = 0.78 P < 0.001

60. Average residence times: Number of foraging strikes / 10 min:

61. P. sicula - Diel variation foraging strikes

62. Conclusions:  The lizards studied regulate their T b with high accuracy and effectiveness  Activity times, diel variation in posturing and in microhabitat use, are to a large extent induced by the interaction with the thermal environment  The needs to thermoregulate may conflict with, or constrain the time devoted to other demands (e.g., foraging)