Seasonal variation in the contribution of different behavioural mechanisms to lizard thermoregulation

Abstract

Summary 1.We studied seasonal changes in the thermoregulatory behaviour of the lacertid lizard Psammodroums algirus in a Mediterranean evergreen forest. Body temperatures ( T b ), environmental operative temperatures ( T e ) and upper and lower limits of the selected thermal range ( T sel ) were lower in May than in July. 2. On average, mean deviations of T b from T sel (0·7 ° C in both seasons) were much smaller than those of T e (8·3 ° C in both seasons). Thus both the accuracy (average difference between T b and T sel ) and effectiveness (the extent to which T b are closer than T e to T sel ) of thermoregulation were high, and similar in both seasons. 3. However the thermoregulatory contribution of two distinct behavioural mechanisms varied markedly between seasons. Daily activity contributed significantly to the regulation of T b in May (when a population of T e thermometers matching lizard activity patterns would be, on average, 1·0 ° C closer to T sel than were randomly available T e ), but not in July (when such a population would be only 0·2 ° C closer to T sel than were randomly available T e ). The selection of sun-shade patches, the contribution of which was larger than that of daily activity in both seasons, was more important in July (when it produced a distribution of T e that would be, on average, 3·1 ° C closer to T sel than were randomly distributed T e ) than in May (when a population of thermometers matching the lizards' pattern of exposure to sunlight would be 1·3 ° C closer to T sel than were randomly available T e ). 4. These changes are discussed in the light of seasonal differences in the daily patterns of among-patch variation in T e . In spring, lizard activity was low in the early morning because even the selection of sunlit patches was of limited utility to attain T b within T sel ; in summer, lizards could remain active at midday, despite low overall thermal suitability, by selecting shaded patches. Thus the contribution of patch selection to thermoregulation was important in the early basking period of both seasons, and at summer midday hours. 5. Our data suggest that shuttling between sun and shade, rather than selecting sun or shade, may be an additional mechanism of behavioural thermoregulation, the importance of which would be greatest at times of day when lizards use patches at random (e.g. spring midday hours), and that their mean T b is closer to the grand mean of full sun and full shade T e than to the mean equilibrium T e within any type of patch.

Thermoregulation in the Andean lizard Anolis heterodermus (Squamata: Dactyloidae) at high elevation in the Eastern Cordillera of Colombia.

“…Seasonal variation of operative temperature of Anolis heterodermus is similar to the results reported in previous other studies, where lowest T e were observed during the winter periods or wet seasons (Hertz et al, 1993;Christian & Bedford, 1995Díaz & Cabezas-Díaz, 2004). Operative temperatures were usually below T b , revealing the poor thermal quality of the environment (d̄e) for this species, particularly during the wet season.…”

“…In contrast to other lizard species (Hertz et al, 1993;Christian & Bedford, 1995Díaz & Cabezas-Díaz, 2004), T b in Anolis heterodermus did not vary between seasons, probably due to the high within variation observed among individuals, and consequent wide T b range (16.6-31.9°C). This observation suggests that A. heterodermus behaves like a eurythermic organism, with a broad range of optimal temperature.…”

“…Species of this genus has been used as model organisms to design a methodology to characterize thermoregulatory strategy in reptiles (Hertz et al, 1993); a protocol widely used since then (Díaz & Cabezas-Díaz, 2004;Blouin-Demers & Nadeau, 2005;Hitchcock & McBrayer, 2006;Row & BlouinDemers, 2006;Herczeg et al, 2008). Studies on Anolis have showed that thermoregulatory strategy varies among species, elevations and seasons, revealing high behavioral and physiological plasticity for dealing with the challenges imposed by the environment (Huey & Webster, 1975;Hertz & Huey, 1981;Hertz, 1981;Hertz et al, 1993;Muñoz et al, 2014).…”

Experimental support for the cost–benefit model of lizard thermoregulation: the effects of predation risk and food supply

“…To test for the extent of thermoregulation we compared individual mean accuracy of thermoregulation with thermal quality of habitat (e.g. Díaz and Cabezas-Díaz 2004). Because the sample sizes of operative temperature measurements were artificial and not independent, we calculated the mean accuracy of thermoregulation for each individual, and simply compared them (for the sexes and treatments separately) with the mean thermal quality of habitat, applying one-sample t tests.…”

Intraspecific Variation of Reproductive Traits in a Mediterranean Lizard: Clutch, Population, and Lineage Effects

“…Terraria were filled with moistened earth covered by leaf litter. A 60 W lamp suspended over one end of the cage created a photothermal gradient (circa 25-50°C) allowing thermoregulation within the preferred temperature range (Díaz and Cabezas-Díaz 2004). Lizards were fed crickets (Acheta domesticus) and mealworms (Tenebrio mollitor), dusted with a commercial vitamin and calcium supplement.…”