Thermoregulatory Precision Research Articles

Seasonal variation of behavioural thermoregulation in a fossorial salamander (Ambystoma maculatum).

Temperature seasonality plays a pivotal role in shaping the thermal biology of ectotherms. However, we still have a limited understanding of how ectotherms maintain thermal balance in the face of varying temperatures, especially in fossorial species. Due to thermal buffering underground, thermal ecology theory predicts relaxed selection pressure over thermoregulation in fossorial ectotherms. As a result, fossorial ectotherms typically show low thermoregulatory precision and low evidence of thermotactic behaviours in laboratory thermal gradients. Here, we evaluated how temperature selection (T sel) and associated behaviours differed between seasons in a fossorial amphibian, the spotted salamander (Ambystoma maculatum). By comparing thermoregulatory parameters between the active and overwintering seasons, we show that A. maculatum engages in active behavioural thermoregulation despite being fossorial. In both seasons, T sel was consistently offset higher than acclimatization temperatures. Thermoregulation differed between seasons, with salamanders having higher T sel and showing greater evidence of thermophilic behaviours in the active compared with the overwintering season. Additionally, our work lends support to experimental assumptions commonly made but seldom tested in thermal biology studies. Ultimately, our study demonstrates that the combination of careful behavioural and thermal biology measurements is a necessary step to better understand the mechanisms that underlie body temperature control in amphibians.

How seasonality influences the thermal biology of lizards with different thermoregulatory strategies: a meta-analysis.

Ectotherms that maintain thermal balance in the face of varying climates should be able to colonise a wide range of habitats. In lizards, thermoregulation usually appears as a variety of behaviours that buffer external influences over physiology. Basking species rely on solar radiation to raise body temperatures and usually show high thermoregulatory precision. By contrast, species that do not bask are often constrained by climatic conditions in their habitats, thus having lower thermoregulatory precision. While much focus has been given to the effects of mean habitat temperatures, relatively less is known about how seasonality affects the thermal biology of lizards on a macroecological scale. Considering the current climate crisis, assessing how lizards cope with temporal variations in environmental temperature is essential to understand better how these organisms will fare under climate change. Activity body temperatures (Tb ) represent the internal temperature of an animal measured in nature during its active period (i.e. realised thermal niche), and preferred body temperatures (Tpref ) are those selected by an animal in a laboratory thermal gradient that lacks thermoregulatory costs (i.e. fundamental thermal niche). Both traits form the bulk of thermal ecology research and are often studied in the context of seasonality. In this study, we used a meta-analysis to test how environmental temperature seasonality influences the seasonal variation in the Tb and Tpref of lizards that differ in thermoregulatory strategy (basking versus non-basking). Based on 333 effect sizes from 137 species, we found that Tb varied over a greater magnitude than Tpref across seasons. Variations in Tb were not influenced by environmental temperature seasonality; however, body size and thermoregulatory strategy mediated Tb responses. Specifically, larger species were subjected to greater seasonal variations in Tb , and basking species endured greater seasonal variations in Tb compared to non-basking species. On the other hand, the seasonal variation in Tpref increased with environmental temperature seasonality regardless of body size. Thermoregulatory strategy also influenced Tpref , suggesting that behaviour has an important role in mediating Tpref responses to seasonal variations in the thermal landscape. After controlling for phylogenetic effects, we showed that Tb and Tpref varied significantly across lizard families. Taken together, our results support the notion that the relationship between thermal biology responses and climatic parameters can be taxon and trait dependent. Our results also showcase the importance of considering ecological and behavioural aspects in macroecological studies. We further highlight current systematic, geographical, and knowledge gaps in thermal ecology research. Our work should benefit those who aim to understand more fully how seasonality shapes thermal biology in lizards, ultimately contributing to the goal of elucidating the evolution of temperature-sensitive traits in ectotherms.

Preliminary Antecedents on the Selected Temperature (Tsel) of Rhinella dpinulosa Wiegmann 1834 (Anura: Bufonidae) from the Andean Environments of Chile

The ambient temperature is a decisive factor in many activities of poikilothermic organisms, since it influences the correct development of their vital processes, which implies the existence of an optimal temperature range. The present study describes selected temperatures (Tsel) of R. spinulosa in adult individuals. For this purpose, adults of this species were acclimatized at 10°C and then subjected to a thermal gradient was used in the laboratory. The mean Tsel in the studied individuals was 23.38±2.65°C, with a range from 17.73°C to 28.93°C. Future surveys are suggested to determine the habitat thermal quality and thermoregulatory precision.

Fecal glucocorticoid metabolites and ectoparasites as biomarkers of heat stress close to roads in a Mediterranean lizard

Differences between air and ground temperatures are expected to narrow with the advance of the season in temperate regions (aka seasonal restriction in the availability of thermal microhabitats), which may activate behavioral and physiological responses of ectotherm species adapted to temperate climates. However, according to cost-benefit models of ectotherm thermoregulation, we hypothesize that these responses may also carry some costs. We quantified seasonal shifts in thermoregulatory precision, concentration of fecal glucocorticoid metabolites, and load of ectoparasites in a Mediterranean lizard, Psammodromus algirus. We also tested whether the proximity to a road, a putative source of chronic stress, can facilitate the glucocorticoid-mediated response of lizards to heat stress. As expected, differences between body and environmental temperatures narrowed during the reproductive season and lizards responded by increasing their thermoregulatory precision and the secretion of glucocorticoids, as indicated by metabolites in feces. Interestingly, lizards tended to have higher glucocorticoid concentration when captured far from the road. This might reflect either a putative impairment of the glucocorticoid-mediated response of the lizards to heat stress close to the road or the plastic capability of P. algirus to acclimate to sources of moderate chronic stress. In the latter direction, the increase of both glucocorticoid metabolites and thermoregulatory precision supported that this Mediterranean species responds to environmental thermal restrictions with adaptive behavioral and physiological mechanisms. However, this was also associated with an increase in its susceptibility to ectoparasites, which represents an added cost to the current cost-benefit models of ectotherm thermoregulation.

Linking behavioral thermoregulation, boldness, and individual state in male Carpetan rock lizards.

Mechanisms affecting consistent interindividual behavioral variation (i.e., animal personality) are of wide scientific interest. In poikilotherms, ambient temperature is one of the most important environmental factors with a direct link to a variety of fitness‐related traits. Recent empirical evidence suggests that individual differences in boldness are linked to behavioral thermoregulation strategy in heliothermic species, as individuals are regularly exposed to predators during basking. Here, we tested for links between behavioral thermoregulation strategy, boldness, and individual state in adult males of the high‐mountain Carpetan rock lizard (Iberolacerta cyreni). Principal component analysis revealed the following latent links in our data: (i) a positive relationship of activity with relative limb length and color brightness (PC1, 23% variation explained), (ii) a negative relationship of thermoregulatory precision with parasite load and risk‐taking (PC2, 20.98% variation explained), and (iii) a negative relationship between preferred body temperature and relative limb length (PC3, 19.23% variation explained). We conclude that differences in boldness and behavioral thermoregulatory strategy could be explained by both stable and labile state variables. The moderate link between behavioral thermoregulatory strategy and risk‐taking personality in our system is plausibly the result of differences in reproductive state of individuals or variation in ecological conditions during the breeding season.

Spatial and Thermal Ecology of Snapping Turtles (Chelydra serpentina) in a Small, Dystrophic Lake in Central Michigan

Understanding the interface between spatial and thermal ecology is integral to understanding energy acquisition and the life histories of ectotherms. Snapping turtles (Chelydra serpentina) occupy a wide range of habitats that vary greatly in their thermal properties. We studied activity, movements, and thermoregulation of C. serpentina in a small, land-locked lake in central Michigan, USA, using radiotelemetry. Consistent with our a priori predictions, turtles were active within core areas along the lake's edge, showed both diurnal and nocturnal activity, and did not make extensive interwetland movements. Turtles left the lake only for nesting or to hibernate in Sphagnum peat or in the banks of a nearby stream. Home range and core area size estimates of C. serpentina were small compared with other previously studied populations, perhaps in part because of the small dimensions of our lake. Contrary to our prediction of a broad Tset (thermoregulatory set-point) range for a large-bodied, habitat generalist turtle, we found a comparatively low and narrow laboratory-determined Tset range (22°C–26°C). Turtle body temperatures (Tb) cycled between May and August and attained maximal values during the evening hours, a pattern that likely results from thermal inertia, the selection of aquatic thermal patches, or both, as Te (operative temperatures) declined. Turtles most effectively maintained Tb within Tset during July and August when thermal conditions were most favorable. Throughout most of the active season the highly aquatic habits of C. serpentina apparently negated the effects of variations in daily weather conditions and their effects on incoming levels of solar radiation on variation in Tb. However, turtles maintained higher average Tb on sunny days compared with overcast days in April and May, the coolest months of the study. Diel Tb cycling ceased during September and October and average Tb declined despite favorable thermal conditions, at least during September, a pattern that could reflect a downward shift in the Tset range. Comparatively, C. serpentina is less effective at thermoregulating than is a small-bodied species at a similar latitude (Chrysemys picta marginata). Apparently, thermal inertia and lack of atmospheric basking proclivities influenced the thermoregulatory precision in our turtles.

Variation in the thermal ecology of an endemic iguana from Mexico reduces its vulnerability to global warming

The persistence of reptile populations in a specific location is influenced by individuals’ capacity to regulate their body temperatures, among other factors. Anthropogenic climate change may pose a risk to the survival of ectothermic animals due to their dependence on external heat sources to thermoregulate. In this study, we calculated indices of thermal habitat quality, thermoregulatory precision, and thermoregulatory effectiveness for the endemic spiny-tailed iguana Ctenosaura oaxacana. We evaluated these indices and the thermoregulatory behavior of the iguanas in the four types of vegetation that provide the most favorable conditions for thermoregulation. We also performed our experiments during both the wet and dry seasons to capture the full range of thermal conditions available to C. oaxacana over the course of a year. Finally, we evaluated the potential niche for the iguana in the years 2020, 2050, and 2080. Thermoregulation depends on both seasonal and environmental factors in this species. We found that thermoregulation effectiveness in both wet and dry seasons depends not only on the thermal conditions of the immediate environment, but also on the cover vegetation and habitat structure available across the range of habitats the species uses. Thus, heterogeneous habitats with dispersed vegetation may be most suitable for this species’ thermoregulatory strategy. Likewise, niche modeling results suggested that suitable habitat for our study species may continue to be available for the next few decades, despite global warming tendencies, as long as cover vegetation remains unaltered. Our results suggest that thermoregulation is a complex process that cannot be generalized for all ectothermic species inhabiting a given region. We also found that temperature changes are not the only factor one must consider when estimating the risk of species loss. To understand the necessary thermal conditions and extinction risk for any ectothermic species, it is necessary to focus studies on the species’ general ecology.

How to avoid errors when quantifying thermal environments

SummaryModelling thermal environments at high resolution becomes simpler when using operative temperature, which condenses microclimate and morphology into an index of thermal stress. Operative temperature can be mapped using large numbers of ‘operative temperature thermometers’, hollow models that duplicate external properties of the animal.As climatologists predict that air will warm by 2–4 °C by 2100, biologists must be able to distinguish climate change from systematic errors in operative temperature of the same magnitude.A systematic error in operative temperature of 2 °C or a similar amount of climate warming can change predicted surface activity and indices of habitat quality, thermoregulatory precision and predation risk by 5–12%, and in some cases more than 30%.As construction details of operative temperature thermometers can affect their accuracy by 2 °C or more, biologists should use detailed physical models calibrated against living animals over potential ranges of postures, orientations and microclimates.Water‐filled models do not measure operative temperature correctly, fail to capture thermal extremes and are an unnecessary complication as one can easily compute the body temperature of moving or stationary animals from body mass and the spatio‐temporal distribution of operative temperatures.

Thermoregulation and aggregation in neonatal bearded dragons ( Pogona vitticeps)

Ectothermic vertebrates, such as reptiles, thermoregulate behaviorally by choosing from available temperatures in their environment. As neonates, bearded dragons ( Pogona vitticeps) are often observed to aggregate in vertical strata. A proximate mechanism for this behavior is the thermal advantage of heat storage ( i.e., grouped lizards benefit through a decreased surface area to volume ratio), although competition for limited thermal resources, or aggregation for social reasons are alternative explanations. This study was designed to gain an understanding of how aggregation and thermoregulation interact. We observed that both isolated and grouped individuals achieved a similar level of thermoregulation (mean T b over trial) within a thermal gradient, but that individuals within a group had lower thermoregulatory precision. An experimental design in which light and ambient temperature ( T a) (20 versus 30 °C) were altered established that a light bulb (source of heat) was a limited and valuable resource to both isolated and grouped neonatal lizards. Lizards aggregated more when the light was on at both temperatures, suggesting that individuals were equally attracted to or repelled from the heat source, depending on the ambient temperature. These data suggest aggregation occurs in neonatal bearded dragons through mutual attraction to a common resource. Further, increased variability in thermal preference occurs in groups, demonstrating the potential for agonistic behaviors to compromise optimal thermoregulation in competitive situations, potentially leading to segregation, rather than aggregation.

The Effect of Thermal Quality on the Thermoregulatory Behavior of the Bearded DragonPogona vitticeps: Influences of Methodological Assessment

Metabolic functions are generally optimized within a narrow range of body temperatures (T(b)'s), conferring thermoregulation great importance to the survival and fitness of an animal. In lizards, T(b) regulation is mainly behavioral, and the metabolic costs associated with behavioral thermoregulation are primarily locomotory. In reptiles, however, it has been proposed that they thermoregulate less precisely when the associated costs, metabolic or otherwise, are high. Such a strategy enhances fitness by allowing lizards to be more flexible to changing environmental conditions while maximizing the benefits of maintaining a high T(b) and minimizing energy expenditure. We evaluated the behavioral thermoregulation of inland bearded dragons Pogona vitticeps under various thermal quality conditions requiring different locomotory investment for thermoregulation. The selected ambient temperature and preferred T(b) ranges increased at lower environmental thermal qualities, indicating a decrease in thermoregulatory precision in environments where the costs associated with thermoregulation were high. The level of thermoregulation was also affected, exhibiting a decrease in preferred T(b) of approximately 2 degrees C at the lowest-thermal-quality treatment. These data provide important implications for the procedural assessment of preferred T(b) and a better understanding of thermal set points in reptiles in general. Our results emphasize that the precise maintenance and assessment of preferred T(b) is contingent on the quality of the environment, laboratory or natural, that the animal inhabits.

Decreased thermoregulatory precision contributes to the hypoxic decrease in body temperature in lizards

Low oxygen induces a decrease in body temperature (Tb) in most vertebrates. This response has been attributed to a decrease in the in the Tb set‐point, protecting organs from oxygen depletion. In addition, hypoxia decreases activity levels and, therefore, the propensity to move. In ectotherms, where thermoregulation is mainly behavioural, hypoxia is, thus, expected to impact the precision of thermoregulatory control. To determine if thermoregulatory precision is indeed decreased in hypoxia, we evaluated the variability and level of thermoregulation of bearded dragons at five oxygen levels in three different experimental settings: a dynamic temperature‐choice shuttle box, a constant temperature dual‐choice shuttle box, and a thermal gradient. A significant increase in the size of the Tb range was observed at the lowest oxygen level (4% O2) in the dynamic shuttle box, but not in the thermal gradient. This was accompanied by a Tb drop of 2‐ 4°C, the drop being greatest when Tb must be actively defended. Situations that force lizards to continually choose temperatures lead to an increase in Tb variability, which is further exaggerated in hypoxia. This study reveals that a decrease in thermoregulatory precision caused by a diminished propensity to move or effect appropriate thermoregulatory responses may partially explain the lowering of Tb observed in hypoxic ectotherms.

Decreased precision contributes to the hypoxic thermoregulatory response in lizards

The decrease in body temperature (T(b)) observed in most vertebrate classes in response to hypoxia has been attributed to a regulated decrease in set-point, protecting organs against tissue death due to oxygen depletion. Hypoxia, however, imparts particular challenges to metabolic function which may, in turn, affect thermoregulation. In ectotherms, where thermoregulation is mainly behavioural, stressors that influence the propensity to move and respond to temperature gradients are expected to have an impact on thermoregulatory control. Using low oxygen as a potent stressor, we evaluated the variability and level of thermoregulation of inland bearded dragons. To examine the source of thermoregulatory variability, we studied their behaviour in an electronically controlled temperature-choice shuttle box, a constant temperature dual-choice shuttle box, and a linear thermal gradient. A significant increase in the size of the T(b) range was observed at the lowest oxygen concentration (4% O(2)), reflecting a decrease in thermoregulatory precision in the temperature-choice shuttle box. This was also accompanied by a drop of approximately 2-4 degrees C in T(b), the drop being greatest in situations where T(b) must be actively defended. Situations that force the lizards to continually choose temperatures, rather than passively remain at a given temperature, lead to an increase in the variability in the manifested T(b), which is further exaggerated in hypoxia. This study reveals that a decrease in thermoregulatory precision caused by a diminished propensity to move or effect appropriate thermoregulatory responses may be a contributing component in the lowering of selected body temperatures observed in many hypoxic ectotherms.

Null models and the thermal biology of the anguid lizard Anguis fragilis; evidence for thermoregulation?

AbstractObservations were made on the behaviour and body temperatures of the legless lizard Anguis fragilis when active above ground in outdoor enclosures. The lizards were most frequently observed in partially shaded locations followed by fully shaded areas; full basking and locomotory movement were minor activities irrespective of weather conditions. Weather conditions had no significant influence on behaviour. Tests for thermoregulation using null models indicated that the main reason for movement above ground was thermoregulatory. Body temperatures were significantly higher than shade operative temperatures but lower than operative temperatures in open locations whatever the weather. Standard deviations in body temperature, employed as a measure of thermoregulatory precision, were lower than standard deviations of operative temperatures in sunny weather but not significantly different from operative temperatures during overcast weather or shaded operative temperatures during sunny weather. The limited amount of locomotory movement suggests thermoregulation was achieved through selection of appropriate microenvironments.

The Evolution of Endothermy and Its Diversity in Mammals and Birds

Many elements of mammalian and avian thermoregulatory mechanisms are present in reptiles, and the changes involved in the transition to endothermy are more quantitative than qualitative. Drawing on our experience with reptiles and echidnas, we comment on that transition and on current theories about how it occurred. The theories divide into two categories, depending on whether selection pressures operated directly or indirectly on mechanisms producing heat. Both categories of theories focus on explaining the evolution of homeothermic endothermy but ignore heterothermy. However, noting that hibernation and torpor are almost certainly plesiomorphic (=ancestral, primitive), and that heterothermy is very common among endotherms, we propose that homeothermic endothermy evolved via heterothermy, with the earliest protoendotherms being facultatively endothermic and retaining their ectothermic capacity for "constitutional eurythermy." Thus, unlike current models for the evolution of endothermy that assume that hibernation and torpor are specialisations arising from homeothermic ancestry, and therefore irrelevant, we consider that they are central. We note the sophistication of thermoregulatory behavior and control in reptiles, including precise control over conductance, and argue that brooding endothermy seen in some otherwise ectothermic Boidae suggests an incipient capacity for facultative endothermy in reptiles. We suggest that the earliest insulation in protoendotherms may have been internal, arising from redistribution of the fat bodies that are typical of reptiles. We note that short-beaked echidnas provide a useful living model of what an (advanced) protoendotherm may have been like. Echidnas have the advantages of endothermy, including the capacity for homeothermic endothermy during incubation, but are very relaxed in their thermoregulatory precision and minimise energetic costs by using ectothermy facultatively when entering short- or long-term torpor. They also have a substantial layer of internal dorsal insulation. We favor theories about the evolution of endothermy that invoke direct selection for the benefits conferred by warmth, such as expanding daily activity into the night, higher capacities for sustained activity, higher digestion rates, climatic range expansion, and, not unrelated, control over incubation temperature and the benefits for parental care. We present an indicative, stepwise schema in which observed patterns of body temperature are a consequence of selection pressures, the underlying mechanisms, and energy optimization, and in which homeothermy results when it is energetically desirable rather than as the logical endpoint.

Thermoregulation in the box turtles Terrapene carolina and Terrapene ornata

Terrapene ornata and Terrapene carolina are box turtles that live in different habitats, the former in grasslands and desert edges and the latter in forested areas. Considering these species' habitat selection, we predicted that T. ornata would select a higher body temperature (Tb) and would be a more precise thermoregulator than T. carolina. We recorded time series of cloacal Tb's in thigmothermal linear gradients from acclimatized (12 h light : 12 h dark; 10 or 20°C) box turtles. We used three analytical methods to evaluate and characterize turtles' activity: a ratio-dependent index that measured activity as an indirect function of changes in Tb, a comparison of hourly mean variances of Tb (ratio-independent), and autocorrelation. We tested the thermoregulatory differences between active T. carolina and T. ornata with a factorial ANOVA and characterized the turtles' thermoregulatory cycles with correlograms. Overall, T. ornata had significantly higher mean Tb's than T. carolina. The two species had similar diel thermoregulatory cycles with a period of approximately 24 h. No clear differences in absolute thermoregulatory precision of Tb's were detected. These species' thermal behaviours were consistent with those reported from field studies, suggesting that there are intrinsically determined differences in thermal preference that may help explain the different habitat choices.

The effect of shielding the parietal eye of Podarcis muralis on behavioral thermoregulation

1. 1. Body temperatures ( T bs) and thermoregulatory precision of 7 sham shielded and 7 parietal eye shielded Podarcis muralis were measured in a linear thigmothermal gradient over a 24 h period. 2. 2. Shielding the parietal eye did not alter the mean T b selected over the 24 h period. 3. 3. Both groups selected T bs that did not differ between photophase and scotophase. 4. 4. Shielding the parietal eye did not influence thermoregulatory precision when measured over the 12 h of photophase, but from 0600–1200 h EST parietal eye shielded lizards thermoregulated more precisely than sham shielded lizards.

Temperature selection and thermoregulatory precision of bisexual and parthenogenetic Cnemidophorus lizards from southern Texas, U.S.A.

1. 1. Temperature selection and thermoregulatory precision of male and female Cnemidophorus gularis and females of two clonal complexes of the parthenogenetic species Cnemidophorus laredoensis (LAR-A and LAR-B) in a linear thigmothermal gradient were measured over a 24-h period. 2. 2. All four groups of Cnemidophorus selected similar mean T b s over the 24-h period. 3. 3. Male and female C. gularis and LAR-A selected higher T b s during some hours of photophase than during some hours of scotophase. 4. 4. The pattern of temperature selection during photophase by LAR-A and LAR-B differed in ways that parallel the differences in the diel activity cycle of these two parthenogens. 5. 5. Cnemidophorus gularis is a more precise thermoregulator than either clonal complex of C. laredoensis.

Interaction of Photoperiod, Temperature, Season, and Diel Cycles on the Thermoregulation of Water Snakes (Nerodia rhombifera)

Diamondback water snakes (Nerodia rhombifera) were acclimatized with different photoperiods and temperatures during different seasons. Body temperatures (Tb) were measured at 10-min intervals for two days. In summer, shortened photoperiod alone did not influence the grand mean Tb but reduced the amplitude of the diel cycle. When we decreased acclimation temperature only, a lower mean Tb was selected but the amplitude of daily rhythm remained unchanged. Paradoxical combinations of photoperiod and temperature (e.g., short day length and low temperature in summer season) did not alter overall Tb but did influence the amplitude of the daily cycle. Snakes selected significant higher Tb in summer than in winter. More precise thermoregulation was observed during scotophase than during photophase in summer with normal acclimatization (longer day length, higher temperature). Photoperiod had no effect on thermoregulatory precision, but lower temperature reduced precision.

Lack of postprandial thermophily in diamondback water snakes, Nerodia rhombifera

Abstract We compared the preferred body temperature ( T b ) of fasted and satiated diamondback water snakes ( Nerodia rhombifera ) in linear thigmothermal gradients. We found no significant postprandial thermophily. Thermoregulatory precision varied among 6 days of testing and was most precise during the first day (24–48 hr after feeding).

Thermoregulatory Set Points of the Eurythermic Lizard Elgaria multicarinata

The lizard Elgaria multicarinata exhibits extremely variable body temperatures during ac- tivity (eurythermy). I used operant conditioning to investigate whether this lack of thermoregulatory precision could be attributed to some aspect of the underlying thermoregulatory mechanism. Estimates of upper and lower set point temperatures (USP and LSP, respectively) were obtained by allowing lizards to control the activation of an overhead heat lamp for thermoregulation in an otherwise cool environment. The influence of shelter availability on thermoregulatory behavior was examined by observing lizards with and without a shelter available under the heat lamp. When a shelter was available for the lizard to hide in under the lamp while heating, USP was estimated to be 33.1 (?0.46 SE) C, and LSP 26.0 (?0.62) C, for a difference of 7.1 C. When no such shelter was available, USP was 31.1 (+0.75) C and LSP 25.0 (+0.55) C, for a difference of 6.1 C. The average standard deviation for each set point within individuals was 1.75 for USP and 2.33 for LSP with a shelter available, and 1.31 for USP and 3.15 for LSP when the shelter was not available. These values indicate minor effects of varying levels of exposure while basking, most notably slight declines in set points. The most important finding of the study was that the thermoregulatory set points for E. multicarinata are similar to those estimated for lizards having much narrower ranges of field body temperatures (stenotherms). My findings did not support the hypothesis that the variance in field body temperatures observed for E. multicarinata is largely attributable to an imprecise thermoregulatory mechanism, either due to a large difference between USP and LSP, variation between individuals in the value of either set point, or the poor definition of the set points at the individual level. Instead, the eurythermy observed for this species must be due to responses to one or more proximate environmental conditions.