Skip to main content
Browse Subject Areas

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here.

  • Loading metrics

Dehydration constrains thermoregulation and space use in lizards

  • Marco Sannolo ,

    Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Visualization, Writing – original draft, Writing – review & editing

    Affiliations CIBIO, Research Centre in Biodiversity and Genetic Resources, InBIO, Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, Vairão, Vila do Conde, Portugal, Departamento de Biologia, Faculdade de Ciências da Universidade do Porto, R. Campo Alegre, Porto, Portugal

  • Miguel Angel Carretero

    Roles Conceptualization, Funding acquisition, Methodology, Project administration, Resources, Supervision, Validation, Writing – review & editing

    Affiliation CIBIO, Research Centre in Biodiversity and Genetic Resources, InBIO, Universidade do Porto, Campus de Vairão, Rua Padre Armando Quintas, Vairão, Vila do Conde, Portugal


Climate change is negatively affecting many species. The increase in mean air temperature is often associated with shifts in distribution, changes in phenology, and local extinctions. Other factors that only partially correlate with air temperature, like water shortage, may also contribute to the negative consequences of climate change. Although the effect of temperature on lizards’ ecophysiology is highly studied, many lizards are also at risks of increased water loss and dehydration, which are predicted to increase under climate change. Here we aimed for the first time to explore if lacertid lizards exposed to dehydration thermoregulate less precisely than hydrated lizards and if dehydrated lizards are less active, change the daily pattern of thermoregulation and balance water balance against thermoregulation. We exposed four lizard species with differences in the thermal preference to thermal gradients with or without a source of water. We measured preferred body temperatures, daily pattern of thermoregulation, and the use of space. Dehydration negatively affected thermoregulation in all investigated species. Dehydrated lizards reduced their preferred body temperature and showed a species-specific pattern of hourly change in thermal preference. Furthermore, they more frequently used the colder parts of the gradients and spent more time hidden. Lizards experiencing dehydration may suffer a reduction in survival and fitness because of poor thermoregulation. Similarly, they may spend more time hidden, waiting for more favourable weather conditions. Such inactivity may carry ecological costs especially in those regions that undergo either short or prolonged periods of droughts.


Changing climatic conditions over the past decades are affecting many animal species [1]. As a result, many taxa are experiencing range shifts [2], change in phenology [3], and local extinction [4] among other effects. However, climate change rate is not globally uniform [5], and some regions are experiencing a faster rise in temperature than others [6]. Furthermore, extreme climatic events, like heatwaves [7] and droughts [8] are becoming more common in some regions, like the Mediterranean basin [9]. Similarly, some species are more exposed to climate change either because they live in areas from which they cannot escape, like mountaintops [10], or because they are particularly vulnerable to the effect of rising temperatures and extreme climatic events, like many amphibians [11].

Reptiles depend strongly on the local external environment to maintain their body temperature within a well-defined range in which performance is optimal [12,13]. Lizards are receiving much attention in recent years since they are considered particularly vulnerable to abrupt changes in environmental temperature [14] that might reduce their activity budget [15] and lead to local extinctions [16]. Indeed, lizards appear to be particularly at risk, as some estimate that up to 20% of lizard species may be at risk of extinction by 2080 [16, but see [17] for the role of behaviour and habitat in modulating the effect of climate change in ectotherms]. The increase of air temperature is often used as the primary argument for explaining the adverse effect of climate change on animal populations, including lizards [16, 18]. However, there is only partial support for the increase in air temperature as being the primary cause of species extinction [19]. Other factors, which partially covary with air temperatures, like food and water availability, are likely among the primary variables determining the survival of a given population under climate change [20].

While the thermal ecology and physiology of lizards have been extensively studied for almost a century [13, 21, 22], much less is known on the negative consequences of water shortage on lizard behaviour, ecology, and conservation. At the individual level, for example, a recent experiment conducted in a confined environment showed that the rainfall regime affected lizards’ behaviour and activity. In particular, during dry periods lizards used shaded microhabitats more often, while they were more active in sunny microhabitats following rainfall [23]. In general, it seems that dehydrated lizards select for lower body temperatures, probably to contain water loss [24]. In temperate regions, water shortage or droughts may also affect lizards’ reproduction [25] and development, with yearlings exposed to dry condition showing lower growth and activity rates [26]. At the population level, lizards might be able to physiologically adjust their resistance to water loss in function of the availability of free-standing water [27].

To complicate the matter, a warmer and drier environment may affect lizards in complicated ways since the interactions between thermal and water balance, and how lizards react to optimize them are not clear. For example, a thermoregulating lizard may get dehydrated, which leads to an excessive concentration of plasma solutes [28]. On the other hand, while keeping suboptimal body temperature may prevent dehydration, it also leads to reduced locomotor and foraging performances [29,30]. Furthermore, geographically separated populations or closely related species might react differently to dehydration, reflecting local adaptation or plasticity [27]. Climate change may further blur the picture because some species or populations might be exposed to different patterns of increasing temperature and decreasing water availability. To what extent dehydrated lacertid lizards prioritise either thermoregulation or reducing water loss is still unknown and deserves further investigation.

Here, we aimed to assess the impact of dehydration on lizard thermoregulation. In particular, we quantified the effect of dehydration on lizard thermoregulation using four Podarcis species as a case study (P. bocagei, P. carbonelli P. guadarramae, and P. virescens). These lacertid species form a single clade that originated in the western Iberian Peninsula during the late Miocene [31], in an epoch during which the climate was more humid, cooler, and summer droughts were yet to come [32]. These species have been recently studied regarding thermal ecology [33] and resistance to water loss [34]. For instance, sympatric and sister taxa species differ in both thermal preference and resistance to water loss [33]. Further, these species show notable differences regarding habitat use [35] and morphology [36]. They also differ in their distribution patterns, with P. bocagei and P. carbonelli restricted to areas with Atlantic influence, while P. guadarramae and P. virescens tend to occupy more Mediterranean environments, although they may partially overlap either regionally or locally [37]. Their context of evolutionary history and ecology make Podarcis wall lizards an excellent system to investigate not only the impact of dehydration on thermoregulation, but also its variation across a clade of closely related, yet very distinctive species.

We formulate three testable hypotheses on the consequences of dehydration on thermal ecology of lizards. We expect that (1) dehydrated lizards will reduce their body temperature, to prevent or diminish further water loss, mainly by using more frequently cooler areas or spending more time hiding; that (2) thermoregulation will be more precise (the mean deviation from preferred temperature is smaller) when lizards have access to water (because lizards can optimize thermoregulation); and that (3) dehydrated lizards will be forced to physiologically trade-off body temperature and water retention. When water is not available, if some lizards will keep maintaining body temperatures close to the preferred ones, they will lose more water than those that will reduce their body temperature to avoid further water loss.

Materials and methods

Sampling and housing

Lizards were collected from two localities in Northern Portugal. In each, a pair of species can be found living in syntopy. We sampled P. bocagei and P. guadarramae near Moledo, a coastal region in Viana do Castelo province (41°50’ N, 8°52’ W), while we sampled P. carbonelli and P. virescens in Santa Maria da Feira, in Aveiro province (40°55’ N, 8°32’ W). Sampling spanned most of the activity season for these species in those locations (beginning of April–end of September). We captured only adult males with intact tails, to avoid reproductive status, body condition and ontogeny affecting thermal preferences [38]. We recognised each individual by means of photo-identification, to avoid pseudoreplication [39]. Before the experiment, we measured the snout-vent length (SVL) of each lizard to the nearest 0.01 mm with a digital calliper. We then left lizards undisturbed for 24 h in individual plastic cages (40×25×25 cm) and provided them with a source of water but with no food. After the first 24 h, we moved each lizard to a randomly chosen gradient (see below) for acclimation. We assumed that when the experiment started, lizards were fully hydrated, having had access to unlimited water during the previous 24 h.

Preferred body temperatures

We assessed the preferred body temperatures of lizards in linear thermal gradients following the method of [33]. Thermal gradients were set up in plastic containers (PVC; 100×30×40 cm; Fig 1) using sand as substrate (~1 cm deep). The gradients’ walls were opaque, and lizards could never see each other during the entire duration of the experiment. They were kept in a room at 20°C and illuminated by natural light through a window. A 150 W infrared lamp suspended above one end of each gradient created a range of temperatures from approximately 19 to 68°C (S3 Table). At the cooler end of each gradient, a small plastic box (13×8.5×5.5 cm) provided a refuge. We placed each lizard in a thermal gradient at 19.00 h when lights were off. The following morning, the infrared lights turned on at 08.00 h and turned off again at 19.00 h. On the first day, lizards were left undisturbed to explore the thermal gradient. At the end of the first day, we randomly emptied the water source (a plastic lid, ~13 ml of tap water) from half of the gradients and left it in the other half. On the next (second) day, the lamps were turned on during the same time span. Every hour between 9.30 and 18.30 h (10 measurements) we measured the skin temperature of each lizard by shooting a thermal picture using a FLIR T335 thermal camera (sensitivity: < 0.05°C; accuracy: ± 2% of the reading; IR image resolution: 320×240 pixels; FLIR Systems Inc., Wilsonville, Oregon, USA). For consistency, the same person (MS) shot all the photos. Skin temperatures were extracted from each IR picture using the Spotmeter function in FLIR Tools 5.12 (Copyright 2018 FLIR Systems, Inc;, selecting a spot in the last third of each lizards’ back. This position allowed us to avoid thermal heterogeneity in lizards’ body and correlate well with internal (cloacal) body temperature [33, 40]. At the end of the second day we reversed the treatments (the water was added to those gradients without it and removed from those gradients where it was present) and measured the hourly skin temperatures of each lizard during the following morning as described above.

Fig 1. Scheme of the experimental setting used in this study.

The five sections, 20 cm each, were only virtual and lizards had full access to every spot in the gradient. Just as an example, a lizard is depicted during thermoregulation in the most used section (see results). The two treatments differed only by the water container being full or empty.

Spatial use of the gradients

Along with their main axis, gradients were divided into five sections of 20 cm each, visually identified by narrow strips of tape running along the walls (Fig 1). By dividing each gradient in this manner, we created five virtual sections (plus the refuge) characterized by different available temperatures, to assess whether lizards used the various areas differently depending on the treatment. Upon shooting each IR picture, we noted the position of the lizard inside the gradient, with respect to the five sections. If a lizard was inside the refuge, we noted this as a sixth position. By using such system, we were able to reference the spatial (linear) use of the gradients with a resolution of 20 cm and with one body temperature measurement every hour for each lizard.

Body mass measurements

At the end of the second and third day (after taking the last thermal picture, at ~19.00 h), each lizard was briefly removed from its gradient and weighted to the nearest 0.1 mg using a precision balance (Sartorius M-Pact AX224, Sartorius AG, Goettingen, Germany). After the second day, lizards were released back into the gradients, while after the third day the experiment ended, and we left them for 24 h in individual boxes with water provided ad libitum. Subsequently, all lizards were released back to their respective site of capture. The difference in body weight between the control and experimental day (with or without access to water) was used to calculate the percentage of water loss (divided by the mass of the assumed fully hydrated lizard) for each individual. Since lizards did not have access to food during the entire period of the experiment, we ruled out that faeces (that are usually expelled in association with urine) might contribute to water loss. We confirmed such assumption by inspecting the gradients after the experiment. We were not able to find any residue that might suggest defecation.

Statistical analysis

To quantify the effect of dehydration, species, time of the day and season on thermal preferences, we fitted a mixed-effects model with body temperature as the dependent variable, a triple interaction treatment × species × time plus a double interaction treatment × day of the season as the predictor. Because body temperature may vary non-linearly with time depending on the treatment, the variable “time” was fitted both as linear and quadratic terms, and the statistical difference of the resulting models was tested using log-likelihood ratio tests (LR) with the function anova.lme. The model with time as a quadratic term fitted the data better and hence was used for subsequent analysis (LR = 178.4, P < 0.0001) To account for repeated measures of the same individual and the possible temporal autocorrelation of the measurements, we included and tested for the effect of individual identity as random factor and repeated measures nested within individuals as autocorrelative structure. The difference between the models with and without random effect was significant (LR = 123.8, P < 0.0001) and, hence, random effects were retained. Instead, models with or without autocorrelation structure were not different (LR = 0.833, P = 0.36). Hence, repeated measures were considered as statistically independent in subsequent analysis. The arrangement of the refuge (water, refuge, lamp) may potentially biased the result. In particular, being the refuge in the cool part (as may be expected in nature for lizards living in temperate areas), dehydrated lizards seeking shelter may be forced to hide in a cool place. Hence, we re-run all analysis previously descripted removing the records of hiding lizards. By doing this, we were able to check if the treatment effect was still significant when active-only lizards were considered. The contribution of main factors and their interaction was assessed inspecting t-tables from models’ summary, and the effect size of the treatment was assessed using Cohen’s d [41]. We also fitted a linear model to test for a possible negative interaction between the amount of water loss and the resulting thermal preference (model form: percentage of water loss ~ mean body temperature (when dehydrated) × species, no random effect, each individual used only once). Percentages of water loss accounted for interindividual differences in body size and were normalised using square root (Shapiro-Wilk normality test (W) = 0.99, P = 0.55). We tested the significance of skewness in body temperature using the D’Agostino test. We tested for the decrease in thermoregulation precision by comparing the variances of body temperatures using F-tests. For both D’Agostino and F-tests, we accounted for repeated measures using the function p.adjust, set on 10 replicates and using the correction of [42]. Skewness values, both original and corrected, are reported in S1 Table. We tested if the use of the space was different under the two treatments using Chi-square tests with the R built-in function chisq.test. To test for interspecific differences in SVL and body mass, we used ANOVA. Statistical analysis was run in R version 3.5.0 [43]. We fit mixed-effects models with the nlme library [44], D’Agostino tests with the moments library [45], Cohen’s d effect sizes with the effsize library [46] and figures were produced using the library ggplot2 [47]. Reported values represent mean ± standard deviation (SD) unless otherwise specified.


Preferred body temperatures

We tested 116 individuals, collecting a total of 2320 body temperature measurements (Table 1). When lizards did not have access to water, all species reduced significantly (P. bocagei t-value = 9.114, d.f. = 550, P < 0.0001; P. carbonelli t-value = 7.101, d.f. = 474, P < 0.0001; P. guadarramae t-value = 10.35, d.f. = 596, P < 0.0001; P. virescens t-value = 8.859, d.f. = 607, P < 0.0001; Fig 2) their mean body temperature, as well as the median and the mode of the distribution. When active-only lizards were considered, the treatment effect was still statistically significant (t-value = 2.77, d.f. = 1940, P = 0.0014). Similarly, we found no statistical support for a seasonal effect on thermal preferences when both treatments were considered (t-value = -0.001, d.f. = 2182, P = 0.56). Changes in curves distribution were more marked if mean values are considered (Table 1). The effect sizes (Cohen's d) ranged from moderate to large (Table 1), suggesting that one day without access to water is enough to negatively affect thermal preferences. Even though some species differed from each other in their preferred body temperature when water was available (S2 Table), such differences turned not significant when water was not available. As predicted, all species thermoregulated more precisely when fully hydrated (P. bocagei F-test = 0.292, d.f. = 289, P <0.0001; P. carbonelli F-test = 0.289, d.f. = 249, P <0.0001; P. guadarramae F-test = 0.186, d.f. = 299, P <0.0001; P. virescens F-test = 0.264, d.f. = 319, P <0.0001; Table 1). Furthermore, the effect of dehydration seemed mostly related to the statistical distribution of the data, rather than a shift in the preferred (mean) temperature (note the overlap of the open, dashed arrows in Fig 2). Indeed, body temperatures were left-skewed for all species and in both treatments (P < 0.01 in all cases, S1 Table). However, the skewness of the dehydrated lizards’ body temperature distribution curves increased, while peaks of distribution changed to a lesser extent (Table 1).

Fig 2. Distributions of the body temperatures selected by four lacertid species when water was either available in the gradient (solid lines) or not (dashed lines).

Y-axis represents standardized (density) frequency of use for each body temperature. Closed arrows represent mean values; open arrows represent the modes (see Table 1 for the numerical values).

Table 1. Comparison of mean, median and interquartile range of the preferred body temperature of four lacertid (Podarcis) species when water was either available or not in the gradients.

Values after ± represent the standard deviation. Paired Cohen’s d for the mean difference are calculated after Cohen (1988).

Hourly pattern of body temperatures

When the daily effect of dehydration on thermoregulation was considered, that is, the interaction treatment × time, and we found that its effect was significant for all species (P. bocagei t-value = 3.308, d.f. = 546, P = 0.001; P. carbonelli t-value = 2.769, d.f. = 470, P = 0.006; P. guadarramae t-value = 4.355, d.f. = 565, P < 0.0001; P. virescens t-value = 3.724, d.f. = 603, P = 0.0002). Such a result indicates not only that mean body temperature was different between treatments for all species, but also that such a difference changed along the day (Fig 3). More precisely, when water was not available, all species adopted a strong curvilinear strategy, with higher body temperatures selected during the central part of the day and lower temperature at the beginning and the end of the day. Still, even during the central part of the day, when dehydrated lizards thermoregulated the most, the difference between treatments was still significant at every time interval, as suggested by the 95% C.I. (Fig 3).

Fig 3. Hourly-based body temperature selected by the four lacertid species when water was either available in the gradient (solid lines and dots) or not (dashed lines and triangles).

Vertical bars represent standard errors. Shaded areas represent 95% confidence intervals.

Spatial use of the gradients

All species exploited the gradients differently depending on the treatment (P. bocagei: χ2 = 83.03, d.f. = 5, P < 0.0001; P. carbonelli: χ2 = 40.16, d.f. = 5, P < 0.0001; P. guadarramae: χ2 = 98.4, d.f. = 5, P < 0.0001; P. virescens: χ2 = 48.24, d.f. = 5, P < 0.0001). Lizards under both treatments spent most of their time within 20–40 cm from the lamp (Fig 1 and Fig 4). Such position offered the best spot for thermoregulation, with an environmental temperature of ~30°C (Fig 4; S3 Table and S1 Fig). The hottest spot in the gradient, directly under the lamp, was used more by hydrated lizards. On the contrary, the refuge, situated in the cool part of the gradient, was mainly used by dehydrated lizards (Fig 4). Lizards scarcely used intermediate sections, regardless of the treatment. Thus, they spent most of their time in the most favourable spot for thermoregulation, but when water was available, they also exploited the warmest area of the gradient since dehydration was not a limiting factor for thermoregulation. Conversely, lizards suffering from dehydration often sought refuge inside the shelter.

Fig 4. Spatial use of the gradients of four species of lacertid lizards.

The x-axis represents the six areas into which each gradient was virtually divided. The leftmost part represents the refuge location, while the rightmost position was directly below the heating lamp. The left y-axis represents the available temperature in the gradient for each position (S3 Table and S1 Fig, Supporting Information for details on how it was estimated). The right y-axis represents the count of lizards for each position. Dark grey bars were counts for lizard when water was available in the gradient, while light grey bars represent lizards that had no access to water. The dark triangles represent the mean environmental temperature as measured by dataloggers for each segment of the gradient.

The effect of dehydration on body mass

The four species of lizards differed in SVL (F3,112 = 8.771, P < 0.0001) and initial body mass (F3,112 = 16.6, P < 0.0001). After 24 h of thermoregulation without access to water, all species lost a significant amount of body mass (Table 2). At the end of the experiment, the most dehydrated species, relative to its body mass, was P. carbonelli (11.3%), while the less dehydrated was P. virescens (7.5%; Table 2). The effect size (Cohens’ d) was large for all species, suggesting that 24 h of water shortage are enough for imposing dehydration. The loss of body mass did not solely depend on body size. Indeed, even though the smallest species (P. carbonelli) suffered the most from dehydration, the biggest species (P. bocagei) was not the better in coping with water loss. Such result is reinforced by investigating the species-specific relationship linking water loss (as a proportion of body mass) and preferred temperature (Fig 5). Although this relationship is statistically non-significant for all species (P = 0.37), there is a significant difference in slope for P. bocagei and P. guadarramae (t-value = -1.985, P = 0.0497, d.f. = 108), a pair of sympatric species. This result suggests not only that individuals selecting higher body temperatures do not necessarily loose more water, but also that hydration level may elicit different thermoregulatory responses depending on the examined species.

Fig 5. The species-specific relationship between preferred body temperature and water loss corrected for individual weights.

Table 2. Body mass after 24 h either with or without access to water in the gradients.

Differences in body mass are expressed both in grams and in percentages. Values are rounded to the second decimal value.


The study of thermoregulation, water balance and their interaction are of primary importance for a better understanding of how ectotherm species interact with their environment [12, 13]. Research on ecophysiology becomes even more compelling when one considers the evidence on how climate change is affecting ectotherms distribution and survival [1, 3, 10, 16]. Our results show that hydration state affects or interacts with thermoregulation. In the present case, dehydration led to reduced body temperature, increased skewness in body temperature distribution, changes in the hourly pattern of thermoregulation and the use of space. Hence, hydration state may interact with thermoregulation and possibly impose a physiological choice between thermoregulation and water balance.

Effects of dehydration on preferred body temperature

Despite having the same thermal availability, dehydrated lizards were, on average, colder than hydrated ones and such difference may affect several aspects of lizards’ ecology. Lower body temperature may be detrimental to the ectotherms’ whole-individual performance as feeding, locomotion, reproduction, social interactions, as well as predator avoidance, all depend on the maintenance of optimal body temperature [22, 48, 49, 50]. In nature, dehydrated lizards may reduce activity, or under droughts, they may reduce activity to prevent dehydration. For example, it has been shown that lizards experiencing droughts are less active than those exposed to milder conditions [23]. As a consequence of reduced activity, lizards may face negative consequences concerning development, survival, and reproduction.

Here, dehydrated lizards also showed an increased skewness in body temperature distribution (Fig 2). Left-skewness in ectotherms body temperature is a well-known phenomenon that is expected for several reasons, like asymmetry in operative temperatures and thermal performance curves [51, 52, 53]. More broadly, skewness is an intrinsic feature of physiological processes, since they increase exponentially with temperature [54]. Recently, an extensive review of skewness in several desert lizard species concluded that left-skewness is common across geography and phylogeny, and does not correlate with body size or median body temperature [55]. Our results reinforce such a view, and the four species we tested reacted in a similar way to water deprivation (Fig 2). Heavily left-skewed body temperature distribution was mainly caused by the time they spent in unfavourabled thermal conditions (especially hiding inside the refuge). Thus, in the present case, dehydration directly affected the lizards’ thermoregulation processes, by limiting their ability to achieve and maintain their preferred body temperature.

Change in daily pattern of thermoregulation

The second result of this study concerns the daily pattern of thermoregulation. Lizards were able to keep high body temperature throughout the day as long as dehydration was not a limiting factor. The same individuals, however, selected lower body temperatures when dehydrated. All species kept lower body temperatures at the beginning and the end of the day, while they raised their body temperature during the middle part of the day. Even at their maximum, body temperatures of dehydrated lizards were always lower than those of hydrated lizards. Since lizards spent only one day in the lab before experimentation (with access to natural light), they likely remained synchronised with circadian rhythm. This result could thus reflect an attempt to thermoregulate only during the hottest part of the day when perhaps the probability of finding preys (and thus replenish water) is the highest. Such a strategy would be related to the concept of hours in restriction of activity [16], postulating that lizards exposed to extremely high environmental temperature will be forced to reduce their activity to dawn and sunset. Our results, however, suggest that lizards tried to maximise thermoregulation during the central part of the day. For ectotherms living in temperate areas experiencing summer droughts, this strategy may conflict with excessively high environmental temperature. Indeed, during summer, many species of European lizards shift to a bimodal pattern of activity [56, 57]. We thus suggest that, on a daily basis, thermoregulation and water balance may occasionally conflict, likely because of the complex interaction between foraging behaviour and the physiological balance of heat and water.

Dehydration constrains the use of space

In the gradients, lizards had access to a wide range of available temperatures and a refuge. In both treatments, lizards spent most of their time in the position that offered the best spot for thermoregulation. The main difference was reflected in the use of gradient extremes, hot and cold. Dehydrated lizards were more prone to use the refuge, while fully hydrated ones spent more time under the lamp. A similar result was found in Sceloporus lizards, which buried more often when dehydrated [24]. Such behavioural differences may result from the attempt of dehydrated lizards to both thermoregulate and avoid water loss. Indeed, even under dehydration, lizards still selected the best spot for thermoregulation, but it is likely that they evaluated the water loss more carefully and retreated more often. An alternative explanation would be that dehydrated lizards had lower temperature because were searching for water instead of thermoregulating. However, our results do not support such a hypothesis, since dehydrated lizards most of the time selected the same spot fully hydrated ones or retreated. Interestingly, when water loss was not a constraint, lizards used the hottest spot in the gradients more often. This behaviour may maximise the heat intake per a given unit of time in a situation in which individuals could indefinitely replenish the water lost through evaporation. This offers a hypothesis testable in the field. Lizards subjected to higher water stress should refrain from reaching a high body temperature or from maintaining it for prolonged periods of time. Other ecological consequences of a reduced availability of suitable habitats may involve increasing intraspecific competition and limited opportunities to find food items and mates.

Interspecific differences

Dehydration elicited behavioural responses that appear to be qualitatively similar in the four species we tested. All species decreased the mean body temperature, levelling on similar values. Even the sympatric pair P. bocagei and P. guadarramae, that differed in preferred body temperature when hydrated (S2 Table), showed no difference under dehydration. Similarly, all species showed a linear or nearly linear trend in daily thermoregulation when fully hydrated but switched to a parabolic trend when dehydrated and retreated more often in the refuge when dehydrated (Fig 3). However, some species differed in the slope of the regression between the preferred temperature and the body mass lost (Fig 5). In particular, P. bocagei and P. guadarramae showed a significant difference in their slopes, suggesting that the negative effects of dehydration on thermoregulation are species-specific, and may differ even in sympatric sister species. Indeed, while in P. guadarramae the loss of water was positively associated with preferred body temperature, the reverse was true for P. bocagei. Interestingly, the other pair of sister species tested, P. carbonelli and P. virescens, showed no differences both in thermal preferences and in the regression slope between the preferred temperature and the body mass lost, despite the fact that the distributions of these two species overlap only over a narrow strip along the costal Portugal [37]. These results reinforce recent findings suggesting that in sympatric lacertid species water balance may often be prioritized, with a potential detrimental effect on thermoregulation. However, the daily and seasonal dynamics may greatly differ depending on the species and environments considered [34, 58, 59].

Thermoregulation is compromised by dehydration

Combining the evidence collected, it appears that hydration level interacts with thermoregulatory behaviour by inducing an adjustment in the distribution of the selected body temperatures. When lizards had full access to water and dehydration posed no restrictions, they optimised thermoregulation, kept a constant body temperature throughout the day, and basked even in the hottest part of the gradients. Optimizing water balance would instead imply refraining from activity and retreating to the coolest spot available since in reptiles both activity level and body temperature determine the rate of water loss [60]. Dehydrated lizards, however, did not cease activity, nor selected the lowest body temperature possible. Instead, they employed a mixed-strategy, thermoregulating at lower temperatures and more often seeking shelter in the refuge. Why dehydrated lizards did not maximize water balance? We speculate that total inactivity would not represent a solution for dehydrated lizards. Instead, a mixed strategy of thermoregulation and retreat may offer more chances to find prey items or free-standing water, and other lizard species show increased activity when rainfall occurs after extended dry periods [61]. Such a strategy, however, may be inadequate under chronic water shortage, such as during European summer droughts [9].

Dehydration and thermal preferences estimation

Our results also bear some implications for the quantification of thermal preferences under laboratory conditions, even though it should be considered that our experiment lasted overall three days—with one day of water deprivation—instead of the typical single one. Usually, lizards being tested in thermal gradients are not provided with water, because some definitions of thermal gradients stated that they should provide an environment free from ecological costs and constraints [62, 63]. Few authors justified the choice to not provide water if the studied species is insensitive to water loss in the short term [64]. We believe that such awareness is still rare and, given the results obtained here, we advise for caution. If the thermal preferences of the studied species are entirely unknown, or if its ecology, physiology, or distribution suggest that it may be sensitive to water loss, providing water in the gradients should be considered. Otherwise, a waterless gradient would violate the assumption that it should be cost-free environment. Furthermore, collected data on thermal preferences, although internally coherent, might be left-skewed due to the interaction between thermal preference and dehydration, and might underestimate preferred temperature.

Some practical aspects may limit the insights that this study provides about the effect of dehydration on thermoregulation. Firstly, we assumed that lizards were fully hydrated at the beginning of the experiment since they had had full access to an unlimited source of water. However, we cannot prove this assumption. Thus, our estimate of water loss reflects the percentage of body mass that each lizard lost under dehydration. Secondly, the effects of dehydration, as quantified in laboratory conditions, may be different under natural conditions. For instance, air temperature and humidity were kept constant in this study and did not fluctuated as they do naturally under circadian rhythms. Thirdly, we focused on the short-term effects of dehydration, and the results of this study cannot be readily extrapolated to infer chronic (e.g., seasonal or annual) stress. Finally, for practical reasons, we investigated the use of space in a confined setting that by necessity is an oversimplification of a natural environment. We believe, however, that such limitations did not prevent us to accurately measure how dehydration affects thermoregulation in lizards.


The present study shows that dehydration may negatively affect thermoregulation in lacertid lizards by forcing them to select body temperatures lower than the preferred ones. Poor thermoregulation may have profound consequences on survival, fitness, and life-history traits in ectotherms [22, 25, 26]. We showed here that dehydrated lizards often selected lower body temperatures more than the preferred ones, thermoregulate less precisely, and change the use of space. Available data on recent climatic scenarios, as well as predictions on future ones, indicate not only a trend in rising temperatures [65] but also an increase in the frequency of extreme heatwaves and droughts, at least for specific regions, like Europe [7, 8]. Temperate reptiles, like the lacertid lizards used in the present study, may be particularly vulnerable to such shortages in water availability since they appear to cope poorly with such climatic extremes [23]. Future research should pose considerable attention on the short and long-term effect that water shortage may impose on wild populations of ectotherms.

Supporting information

S1 Fig. Environmental temperature in the gradients.

Boxplot of environmental temperatures available in the gradients as measured with dataloggers. At the end of the experiment, we randomly chose two gradients. In each, we placed six iButton Thermochron (Model DS1923; Maxim Integrated Products, Sunnyvale, CA, USA). Each datalogger was positioned in the middle of each of the five sections into which the gradients were virtually divided. The sixth datalogger was placed inside the refuge. Each datalogger was 20 cm away from the next, except the first one, that was close (~ 7 cm) to the one positioned inside the refuge. Dataloggers were set to record temperature every 30 mins and were retrieved after seven days. We merged the data from the two gradients and of the six positions to create a distribution of temperature for each section of the gradients.


S1 Table. Skewness in preferred body temperature in four species of Podarcis lizards subjected to two treatments.

In “water” treatment, individuals had had full access to a water source throughout the experiment. On the contrary, a water source was not available during the “no water” treatment. Skewness was calculated for both treatment, and its statistical significance tested with D’Agostino test. Original P-values are reported as well as corrected ones for multiple individual measurements (for each lizard body temperature was measured ten times).


S2 Table. Interspecific differences in reaction to dehydration.

Even though some of the tested species differ in their thermal preference when fully hydrated, their body temperature did not differ when dehydrated. Such a result suggests that, despite having different thermal ecology under optimal conditions, dehydration likely impose similar physiological constrains on all tested species, forcing them to converge on comparable, lower body temperatures.


S3 Table. Environmental temperature in the gradients.

Mean environmental temperatures ± standard deviation for each section of the gradient.



We would like to thank Raquel Ponti for the precious help in the field, Memeo for the invaluable company during the drafting of the manuscript and Frederico Barroso and Ofir Levy for revising it before submission. Barry Sinervo and an anonymous reviewer provided valuable comments on a earlier draft of the manuscript. Permits for lizards capturing and handling were provided by the Instituto da Conservação da Natureza e das Florestas (ICNF Portugal, no. 576/2017/CAPT). Experiments followed the ethical guidelines of the University of Porto.


  1. 1. Parmesan C. Ecological and evolutionary responses to recent climate change. Annual Review of Ecology, Evolution, and Systematics. 2006; 37:637–669.
  2. 2. Moritz C, Patton JL, Conroy CJ, Parra JL, White GC, Beissinger SR. Impact of a century of climate change on small mammal communities in Yosemite National Park, USA. Science. 2008; 322:261–264. pmid:18845755
  3. 3. Parmesan C, Yohe G. A globally coherent fingerprint of climate change impacts across natural systems. Nature. 2003; 421:37–42. pmid:12511946
  4. 4. Wiens JJ. Climate-related local extinctions are already widespread among plant and animal species. PLOS Biology. 2016; 14:1–18.
  5. 5. Urban MC. Accelerating extinction risk from climate change. Nature. 2015; 348:571–573
  6. 6. Loarie SR, Duffy PB, Hamilton H, Asner GP, Field CB, Ackerly DD. The velocity of climate change. Nature. 2009; 462:1052–1055. pmid:20033047
  7. 7. Schär C, Vidale PL, Lüthi D, Frei C, Häberli C, Liniger MA, et al. The role of increasing temperature variability in European summer heatwaves. Nature. 2004; 427:332–336. pmid:14716318
  8. 8. Dai A. Increasing drought under global warming in observations and models. Nat Clim Change. 2013; 3:52–58.
  9. 9. Rahmstorf S, Coumou D. Increase of extreme events in a warming world. Proc Nat Acad Sci USA. 2011; 108:17905–17909. pmid:22025683
  10. 10. Huey RB, Deutsch CA, Tewksbury JJ, Vitt LJ, Hertz PE, Alvarez Pérez HJ, et al. Why tropical forest lizards are vulnerable to climate warming. Proc R Soc Lond B Biol Sci. 2009; 276:1939–48.
  11. 11. Kiesecker JM, Blaustein AR, Belden LK. Complex causes of amphibians population declines. Nature. 2001; 410:681–684. pmid:11287952
  12. 12. Huey RB. Temperature, physiology and the ecology of reptiles. In: Gans C, Pough FH, editors. Biology of the Reptilia. Academic Press, London; 1982. pp. 25–91.
  13. 13. Angilletta MJ. Thermal Adaptation: A Theoretical and Empirical Synthesis. Oxford University Press Inc New York, USA; 2009.
  14. 14. Huey RB, Losos JB, Moritz C. Are lizards toast? Science. 2010; 328:832–833. pmid:20466909
  15. 15. Deutsch CA, Tewksbury JJ, Huey RB, Sheldon KS, Ghalambor CK, Haak DC, et al. Impacts of climate warming on terrestrial ectotherms across latitude. Proc Natl Acad Sci USA. 2008; 105:6668–6672. pmid:18458348
  16. 16. Sinervo B, Méndez-de-la-Cruz F, Miles DB, Heulin B, Bastiaans E, Villagrán-Santa Cruz M, et al. Erosion of lizard diversity by climate change and altered thermal niches. Science. 2010; 328:894–899. pmid:20466932
  17. 17. Huey RB, Kearney MR, Krockenberger A, Holtum JAM, Jess M, Williams SE. Predicting organismal vulnerability to climate warming: roles of behaviour, physiology and adaptation. Philos Trans R Soc Lond B Biol Sci. 2012; 367:1665–79- pmid:22566674
  18. 18. Rosenzweig C, Karoly D, Vicarelli M, Neofotis P, Wu Q, Casassa G, et al. Attributing physical and biological impacts to anthropogenic climate change. Nature. 2008; 453:353–357. pmid:18480817
  19. 19. Cahill AE, Aiello-Lammens ME, Fisher-Reid MC, Hua X, Karanewsky CJ, Yeong Ryu H, et al. How does climate change cause extinction? Proc R Soc Lond B Biol Sci. 2012; 280:20121890–20121890.
  20. 20. McLaughlin JF, Hellmann JJ, Boggs CL, Ehrlich PR. Climate change hastens population extinctions. Proc Natl Acad Sci USA. 2002; 99:6070–6074. pmid:11972020
  21. 21. Cowles RB, Bogert CM. A preliminary study of the thermal requirements of desert reptiles. Bull Am Mus Nat Hist. 1944; 83:261–296.
  22. 22. Angilletta MJ, Niewiarowski PH, Navas CA. The evolution of thermal physiology in ectotherms. J Therm Biol. 2002; 27:249–268.
  23. 23. Ryan MJ, Latella IM, Giermakowski JT, Snell H, Poe S, Pangle RE, et al. Too dry for lizards: short-term rainfall influence on lizard microhabitat use in an experimental rainfall manipulation within a piñon-juniper. Funct Ecol. 2016; 30:964–973.
  24. 24. Crowley S. The effect of desiccation upon the preferred body temperature and activity level of the lizard Sceloporus undulatus. Copeia. 1987; 1987:25–32.
  25. 25. Wang Y, Gao Z, Shu Z, Li R, Huai J, Wei B, et al. Low precipitation aggravates the impact of extreme high temperatures on lizard reproduction. Oecologia. 2016; 182:961–971. pmid:27638182
  26. 26. Lorenzon P, Clobert J, Oppliger A, John-Adler H. Effect of water constraint on growth rate, activiity and body temperature of yearling common lizard. Oecologia. 1999; 118:423–430. pmid:28307409
  27. 27. Dupoué A, Rutschmann A, Le Galliard JF, Miles DB, Clobert J, DeNardo DF, et al. Water availability and environmental temperature correlate with geographic variation in water balance in common lizards. Oecologia. 2017; 185:561–571. pmid:29018996
  28. 28. Minnich JE. The use of water. In: Biology of the Reptilia. Academic Press, London; 1982.pp. 325–395.
  29. 29. Avery RA, Mynott A. The effects of temperature on prey handling time in the common lizard, Lacerta vivipara. Amphibia-Reptilia. 1990; 11:111–122.
  30. 30. Angilletta MJ, Hill T, Robson MA. Is physiological performance optimized by thermoregulatory behavior?: a case study of the eastern fence lizard, Sceloporus undulatus. J Therm Biol. 2002; 27:199–204.
  31. 31. Kaliontzopoulou A, Pinho C, Harris DJ, Carretero MA. When cryptic diversity blurs the picture: a cautionary tale from Iberian and North African Podarcis wall lizards. Biol J Linn Soc. 2011; 103:779–800.
  32. 32. Jiménez-Moreno G, Fauquette S, Suc JP. Miocene to Pliocene vegetation reconstruction and climate estimates in the Iberian Peninsula from pollen data. Rev Palaeobot Palynol. 2010; 162:403–415.
  33. 33. Barroso FM, Carretero MA, Silva F, Sannolo M. Assessing the reliability of thermography to infer internal body temperatures of lizards. J Therm Biol. 2016; 62:90–96. pmid:27839556
  34. 34. Sannolo M, Barroso, FM, Carretero MA. Physiological differences in preferred temperatures and evaporative water loss rates in two sympatric lacertid species. Zoology. 2018; 126:58–64. pmid:29306684
  35. 35. Gomes V, Carretero MA, Kaliontzopoulou A. The relevance of morphology for habitat use and locomotion in two species of wall lizards. Acta Oecol. 2016; 70:87–95.
  36. 36. Kaliontzopoulou A, Carretero MA, Llorente GA. Morphology of the Podarcis wall lizards (Squamata: Lacertidae) from the Iberian Peninsula and North Africa: patterns of variation in a putative cryptic species complex. Zool J Linn Soc. 2012; 164:173–193.
  37. 37. Loureiro A, Ferrand de Almeida N, Carretero MA, Paulo OS. Atlas Dos Anfíbios e Répteis de Portugal. Instituto da Conservação da Natureza e da Biodiversidade, Lisboa, Portugal; 2008.
  38. 38. Carretero MA, Roig JM, Llorente GA. Variation in preferred body temperature in an oviparous population of Lacerta (Zootoca) vivipara. Herpetol J. 2005; 15, 51–55.
  39. 39. Sacchi R, Scali S, Mangiacotti M, Sannolo M, Zuffi MAL. Digital identification and analysis. In: Dodd CK Jr, editor. Reptile Ecology and Conservation, A Handbook of Techniques. Oxford University Press, New York; 2016. pp. 59–72.
  40. 40. Sannolo M, Mangiacotti M, Sacchi R, Scali S. Keeping a cool mind: head–body temperature differences in the common wall lizard. J Zool. 2014; 293:71–79.
  41. 41. Cohen J. Statistical Power Analysis for the Behavioral Sciences. Lawrence Erlbaum Associated, Hillsdale, USA; 1988.
  42. 42. Benjamini Y, Yekutieli D. The control of the false discovery rate in multiple testing under dependency. Ann Stat. 2001; 29:1165–1188.
  43. 43. R Core Team. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria; 2017. Available at:
  44. 44. Pinheiro JC, Bates DM, DebRoy S, Sarkar D. Nlme: Linear and Nonlinear Mixed Effects Models. R Package Version 3.1–129; 2017.
  45. 45. Komsta L., Novomestky F. Moments: Moments, cumulants, skewness, kurtosis and related tests. R package version 0.14; 2015.
  46. 46. Torchiano M. Effsize: Efficient Effect Size Computation. R Package Version 0.7.1; 2017.
  47. 47. Wickham H. ggplot2: Elegant Graphics for Data Analysis. Springer-Verlag, New York; 2009.
  48. 48. Avery HW, Spotila JR, Congdon JD, Fisher RU, Standora EA, Avery SB. Roles in the of diet protein and temperature growth and nutritional of juvenile energetics slider turtles, Trachemys scripta. Physiol Zool. 1993; 66:902–925.
  49. 49. Selong JH, McMahon TE. Effect of temperature on growth and survival of bull trout, with application of an improved method for determining thermal tolerance in fishes. Trans Am Fish Soc. 2001; 130:1026–1037.
  50. 50. Berger D, Walters R, Gotthard K. What limits insect fecundity? Body size- and temperature-dependent egg maturation and oviposition in a butterfly. Funct Ecol. 2008; 22:523–529.
  51. 51. Huey RB, Pianka ER. Seasonal variation in thermoregulatory behavior and body temperature of diurnal Kalahari lizards. Ecology. 1977; 58:1066–1075.
  52. 52. Hertz PE. Evaluating thermal resource partitioning. Oecologia. 1992; 90:127–136. pmid:28312280
  53. 53. Dell AI, Pawar S, Savage VM. Systematic variation in the temperature dependence of physiological and ecological traits. Proc Natl Acad Sci USA. 2011; 108:10591–10596. pmid:21606358
  54. 54. DeWitt CB, Friedman RM. Significance of skewness in ectotherm thermoregulation. Amer Zool. 1979; 19:195–209.
  55. 55. Huey RB,Pianka ER. Body temperature distributions of active diurnal lizards in three deserts: Skewed up or skewed down? Funct Ecol. 2017; 32:334–344.
  56. 56. Foá A, Tosini G, Avery RA. Seasonal and diel cycles of activity in the ruin lizard, Podarcis sicula. Herpetol J. 1992; 2:86–89.
  57. 57. Adamopoulou C, Valakos ED (2005) Thermal ecology and activity cycle of Podarcis milensis in a sandy coastal are. Isr J Zool. 2005; 51:39–52.
  58. 58. García-Muñoz E, Carretero MA. Comparative ecophysiology of two sympatric lizards. Laying the groundwork for mechanistic distribution models. Acta Herpetol. 2013; 8:123–128.
  59. 59. Osojnik N, Žagar A, Carretero MA, García-Muñoz E, Vrezec A. Ecophysiological dissimilarities of two sympatric lizards. Herpetologica. 2013; 69:445–454.
  60. 60. Mautz W. Factors influencing evaporative water loss in lizards. Comp Biochem Physiol A. 1980; 67:429–437.
  61. 61. Rutherford PL, Gregory PT. How age, sex, and reproductive condition affect retreat-site selection and emergence patterns in a temperate-zone lizard, Elgaria coerulea. Ecoscience. 2003; 10:24–32.
  62. 62. Porter W, Gates D. Thermodynamic equilibria of animals with environment. Ecol Monogr. 1969; 39:227–244.
  63. 63. Huey RB, Slatkin M. Cost and benefits of lizard thermoregulation. Q Rev Biol. 1976; 51:363–384. pmid:981504
  64. 64. Rusch TW, Angilletta MJ. Competition during thermoregulation altered the body temperatures and hormone levels of lizards. Funct Ecol. 2017; 31:1519–1528.
  65. 65. IPCC Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri RK, Meyer LA (eds.)]. IPCC, Geneva, Switzerland; 2014. 151 pp.