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Thermoregulation in lizards

Thermoregulation in lizards. Dirk Bauwens. Thermoregulation. What? Why? How should we study it? Examples studies Mechanisms? Interactions other activities. Thermoregulation. what?  definition. target range. Definition thermoregulation:.

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Thermoregulation in lizards

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  1. Thermoregulation in lizards Dirk Bauwens

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

  3. Thermoregulation what?  definition

  4. target range

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

  6. Thermoregulation why?

  7. Thermal sensitivity: The rate of biological processes is temperature dependent TPB80 Topt

  8. Thermal optima in Lacerta vivipara Topt TPB80 body mass change energy- intake gut-passage rate handling rate catching rate sprint speed source: Van Damme et al. 1991 (Funct. Ecol. 5: 507- 517)

  9. Thermoregulation How to study it?

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

  11. Study thermoregulation Requires information on: • Tbs active lizards • Target range (Tsel) • Environmental temperatures • Mechanisms: behaviour / physiology

  12. Study thermoregulation • Body temperatures (Tbs) maintainedduringactivity • Tbs = finalresult of regulatory proces • How measure? • “grabandjab” • telemetry • Obtainmeasurements at different timesandplaces!

  13. Study thermoregulation • Target range for Tbs • Tbs in “ideal” conditionsforregulation • Reflect Topt • How measure? • In thermogradient • Tsel : upper- andlowerlimits (80 of 95%) of Tbs maintained

  14. Study thermoregulation • Environmentaltemperatures • Quantification of heat exchange betweenorganismsandtheir environment

  15. Heat exchange with environment

  16. 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"

  17. Energy Balance Equation Qa = asAsS + asAss + asAgr (S + s) + at(AgRg + AsRa) M-lEb = 0.096 eTb/10 - 0.298 e0.0586Tb M-lEb M-lEb Qa + M - lEb = e s ( Tb - + 273) 4 + H(Tb-Ta- ) K K H = 3.49 (V/D)O.5

  18. 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… • “Tb” of model = Te (“operative environmental temperature”) Tb of nonthermoregulating organism • (Relatively) easy & cheap

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

  20. Study thermoregulation • Tbs active lizards • Target range: Tsel • Environmental temperatures: Te • Behavioural observations (thermo-regulation, social, foraging, …) • Continuous observations (1 lizard – 10 min) • “Scan sampling” (n lizards – 1 sec)

  21. Thermoregulation in lizards • Sunny days • Variation during course of day Examples studies

  22. Podarcis sicula Podarcis muralis European lizards (Lacertidae)

  23. Islas Columbretes(Spain) Palagruža(Croatia)

  24. Agama atra (South-Africa)

  25. Studies thermoregulation How “well” do lizards thermoregulate? • Similarity of Tbs with target range (Tsel): “accuracy” thermoregulation • Deviation of Tbs from operative temperatures (Tes): “effectiveness” thermoregulation

  26. Tsel Podarcis atrata - Body temperatures 10 20 30 40 50 60

  27. Podarcis atrata - Operative temperatures 8 T e 6 Percentage of Observations 4 2 0 10 20 30 40 50 60 Temperature (°C)

  28. Podarcis atrata - Columbretes 60 50 T 40 Temperature (°C) sel 30 20 730 900 1030 1200 1330 1500 1630 1800 Hour

  29. Podarcis sicula - Palagruža

  30. Agama atra – Jonkershoek (ZA)

  31. How “well” do lizards regulate Tb? • Tbs almost always within Tsel : high “accuracy” of thermoregulation • Tbs deviate considerably from Tes: high “effectiveness” of thermoregulation

  32. How do lizards regulate their Tb? What “mechanisms” are used? • Ectotherms: physiologyunimportant • Behaviouralthermoregulation: • Restriction of activitytimes • Postures & orientation • Selectionthermally “suitable” microhabitats

  33. Behavioural thermoregulation • Towhatextent does thermoregulationdeterminelizardbehaviour? • Recall the coppermodels: Te  Tb of non-thermoregulatinglizard • At times / placeswithTeTsellizardscaneasilyattainTbTsel • Let’s look at distributions of Teprovidedbythe coppermodels

  34. Suitability of habitat / time: % models with Te Tsel too warm “ideal” too cold

  35. Behavioural thermoregulation • Towhatextent does thermoregulationdeterminelizardbehaviour? • At times / placeswithTeTsellizardscaneasilyattainTbTsel • Ifthermoregulationdictatesbehaviour, lizardsshouldrestrictactvitytotimes / placeswhere a high % of TeTsel(“onlythermoregulation” hypothesis)

  36. Behavioural thermoregulation Main “mechanisms”: • Restrictionof activitytimes • Postures & orientation • Selectionthermally “suitable” microhabitats

  37. Restriction of activity times • Prediction: activeonlywhen heat loads permit toattainTbs Tsel • Seasonalactivity (hibernation; aestivation) • Diurnal vs. nocturnalactivity • Can we predictdailyactivitytimes? • Activity restrictedtotimeswhenminimalfraction of TesTsel

  38. Prediction activity times

  39. Vaalputs, Karoo Desert (South-Africa)

  40. Cordylus polyzonus

  41. Cordylus polyzonus – Vaalputs (mid summer)

  42. Cordylus polyzonus - Vaalputs (mid-summer)

  43. Prediction activity times • Overall good agreement between observed and predicted • Major discrepancies in early morning • Why differences? • Predictions assume “only thermoregulation” and lizards also do other things (forage, social interactions, …) • Lizards avoid Tbs > Tsel (overheating)

  44. Postures & orientation • Usage of postures & adjustment of orientation • Modify the rate of heat exchange with environment • Increase when Te < Tsel Decrease when Te >Tsel

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