Influence of heat transmission mode on heating rates and on the selection of patches for heating in a mediterranean lizard

State-dependent movement choices of desert lizards: The role of behavioural thermoregulation during summer and winter

Environmental temperatures are increasing worldwide, threatening desert ectotherms already living at their thermal limits. Organisms with flexible thermoregulatory behaviours may be able to mitigate the effects of extreme temperatures by moving among microhabitats, yet little work has tracked movement patterns of desert ectotherms in the wild over diurnal scales or compared behaviour among seasons. Here, we used camera traps to track the thermoregulatory behaviour and microhabitat choices of 30 desert lizards (Messalina bahaldini) in custom, outdoor arenas that provided access to open, rock, and bush microhabitats. We found that in the summer, lizards preferred to move to the shaded microhabitats and remain there under warmer conditions. During winter, however, lizards' activity was not related to temperature, and lizards mostly chose to remain in the open habitat. Interestingly, in both seasons, lizards tended to remain in their current microhabitat and moved infrequently between certain combinations of microhabitats. Our study shows that thermoregulation (shade-seeking behaviour) is a major factor during summer, helping lizards to avoid extreme temperatures, but not during winter, and shows a novel effect of current microhabitat on movement, suggesting that other biotic or abiotic factors may also drive microhabitat choice. Understanding the complex factors at play in microhabitat choice is critical for developing conservation programs that effectively mitigate the negative impacts of climate change on desert animals.

Melanistic coloration does not influence thermoregulation in the crepuscular gecko Eublepharis macularius

Body coloration in ectotherms serves multiple biological functions, including avoiding predators, communicating with conspecific individuals, and involvement in thermoregulation. As ectotherms rely on environmental sources of heat to regulate their internal body temperature, stable melanistic body coloration or color change can be used to increase or decrease heat absorption and heat exchange with the environment. While melanistic coloration for thermoregulation functions to increase solar radiation absorption and consequently heating in many diurnal ectotherms, research on crepuscular and nocturnal ectotherms is lacking. Since crepuscular and nocturnal ectotherms generally absorb heat from the substrate, in these organisms melanistic coloration may have other primary functions beside thermoregulation. As such, in this work we hypothesized that the proportion of dorsal melanistic body coloration would not influence heating and cooling rates in the crepuscular gecko, Eublepharis macularius, and that changes in environmental temperature would not trigger color changes in this species. Temperature measurements of the geckos and of the environment were taken using infrared thermography and temperature loggers. Color data were obtained using objective photography and a newly developed custom software package. We found that body temperature reflected substrate temperatures, and that the proportion of melanistic coloration has no influence on heating or cooling rates or on color changes. These findings support that melanistic coloration in E. macularius may not be used for thermoregulation and strengthen the hypothesis that in animals active in low light conditions, melanistic coloration may be used instead for camouflage or other functions.

Thermal biology of two sympatric Lacertid lizards (Lacerta diplochondrodes and Parvilacerta parva) from Western Anatolia

Sympatric lizard species present convenient models for studying differentiation in thermal behavior and the role of morphological differences in their thermal biology. Here we studied the thermal biology of two sympatric lizard species which occur sympatrically in the Phrygian Valley of Western Anatolia. These two species differ in body size, with Lacerta diplochondrodes being larger than Parvilacerta parva. The surface body temperatures of the individuals belonging to both species were recorded when active in the field. Additionally, several environmental parameters including solar radiation, substrate temperature, air temperature and wind speed were monitored to investigate the relative effects of these abiotic parameters on the thermal biology of the two species. The surface body temperature and temperature excess (difference between body and substrate temperature) of the two species, while being relatively close to each other, showed seasonal differences. Solar radiation, substrate temperature and air temperature were the main factors influencing their thermal biology. Additionally, although body size did not have a direct effect on body temperature or temperature excess, the interaction between body size and solar radiation on temperature excess was significant. In conclusion, our study partially supports the conservation of body temperature of related lizard species.

Can the spectrophotometric response of the elytra explain environmental preferences? A study in seven Onthophagus species (Coleoptera, Scarabaeidae)

Beetles are the most successful and diversified animal taxa characterized by the possession of an external pair of sclerotized wings (elytra). Managing electromagnetic radiations could be one of the functions of the exoskeleton. We studied the spectrophotometric response to ultraviolet, visible, and near-infrared radiations of the elytra of seven closely related and sympatric Onthophagus species to examine if the environmental preferences of these species could be associated with the spectrophotometric behaviour of their elytra. Our results indicated that sibling species can drastically differ in their environmental preferences but not in their spectrophotometric responses. However, our results corroborated that there are interspecific differences in the spectrophotometric characteristics of the elytra, which are mainly explained by morphological features. Among the examined morphological variables, darkness seems to be especially relevant as it facilitates the absorbance and obstructs the transmittance of visible and near-infrared radiations.

Effects of food intake and hydration state on behavioral thermoregulation and locomotor activity in the tropidurid lizard Tropidurus catalanensis

Theoretical models predict that lizards adjust their body temperature through behavioral thermoregulation as a function of food availability. However, behavioral thermoregulation is also governed by interactions among physiological and ecological factors other than food availability, such as hydration state, and sometimes it can even conflict with the locomotor activity of animals. Here, we aimed to investigate the role of food intake and hydration state on behavioral thermoregulation and voluntary locomotor activity in the lizard Tropidurus catalanensis We hypothesized that food intake can influence behavioral thermoregulation via an interaction with hydration state. We also hypothesized that lizards should endeavor to spend as little time as possible to reach their preferred body temperature to defend other physiological and/or ecological functions. We collected lizards in the field and brought them to the laboratory to measure the preferred temperature selected in a thermal gradient and the total distance traveled by them in fed and unfed conditions and with variable hydration state. Our results showed that food consumption was the most important predictor of preferred temperature. In contrast, either the hydration state alone or its interaction with food consumption did not have important effects on the lizards' thermal preference. Also, we found that the total distance traveled by lizards was not affected by food intake and was barely affected by the hydration state. We provide an experimental approach and a robust analysis of the factors that influence behavioral thermoregulation and locomotor activity in a tropical lizard.

Decrease in preferred temperature in response to an immune challenge in lizards from cold environments in Patagonia, Argentina

In ectotherms, the likelihood of surviving an infection is determined by the efficiency of thermoregulation, the availability of a variety of thermal microenvironments, the individual's health status, and the virulence of the infective agent. Physiological and behavioral demands related to an efficient immune response entail a series of costs that compete with other vital activities, specifically energy storage, growth, reproduction, and maintenance functions. Here, we characterize the thermal biology and health status by the presence of injuries, ectoparasites, body condition, and individual immune response capacity (using phytohemagglutinin in a skin-swelling assay) of the southernmost lizards of the world, Liolaemus sarmientoi, endemic to a sub-optimal, cold environment in Patagonia, Argentina. In particular, we study the effect of a bacterial endotoxin (lipopolysaccharide; LPS-treatment) on thermoregulation. We found that the field-active body temperature (T_b) was much lower than the preferred body temperature (T_p) obtained in the laboratory. All the individuals were in good body condition at the beginning of the experiments. The phytohemagglutinin test caused detectable thickening in sole-pads at 2 h and 24 h post-assay in males and non-pregnant females, indicating a significant innate immune response. In the experimental immune challenge, the individuals tended to prefer a low body temperature after LPS-treatment (2 h post-injection) and developed hypothermia, while the control individuals injected with phosphate buffered saline (PBS), maintained their body temperature throughout the trial. In both the LPS-treatment and PBS-control individuals, BC declined during the experiment. Hypothermia may allow this southernmost species to optimize the use of their energetic resources and reduce the costs of thermoregulation in a cold-temperate environment where they rarely attain the mean T_p (35.16 °C) obtained in laboratory.

How and when melanic coloration is an advantage for lizards: the case of three closely-related species of Liolaemus

Body temperature affects various aspects of ectotherm biology. Reptiles, as ectotherms, gain and control their temperature mainly through behavioural adjustments, although some body traits may also be advantageous. According to the thermal melanism hypothesis (TMH) dark colour may be thermally advantageous in cold environments. Additionally, differences in thermoregulatory capacity may also affect performance. We analysed the role of melanism in the thermoregulation and sprint speed performance of three species of Liolaemus lizards from Argentinean Patagonia. Liolaemus shitan, L. elongatus and L. gununakuna are phylogenetically close, with similar body sizes and life history traits, but differ in their melanic colouration, L. shitan being the darkest and L. gununakuna the lightest species. We estimated sprint speed performance curves and heating rates, and recorded final body temperature and sprint speed achieved after a fixed heating time, from two different initial body temperatures, and with and without movement restriction. Performance curves were similar for all the species, but for L. gununakuna the curve was more flattened. Darker species showed faster heating rates, ran faster after fixed heating trials at the lowest temperature, and reached higher body temperatures than L. gununakuna, but this was compensated for by behavioural adjustments of the lighter lizards. Similarity of sprint speed performance may be due to the conservative nature of this character in these species, while variation in heating ability, particularly when starting from low temperatures, may reflect plasticity in this trait. The latter provides support for the TMH in these lizards, as melanism helps them increase their body temperature. This may be especially advantageous at the beginning of the day or on cloudy days, when temperatures are lower.

Crypsis Decreases with Elevation in a Lizard

Predation usually selects for visual crypsis, the colour matching between an animal and its background. Geographic co-variation between animal and background colourations is well known, but how crypsis varies along elevational gradients remains unknown. We predict that dorsal colouration in the lizard Psammodromus algirus should covary with the colour of bare soil—where this lizard is mainly found—along a 2200 m elevational gradient in Sierra Nevada (SE Spain). Moreover, we predict that crypsis should decrease with elevation for two reasons: (1) Predation pressure typically decreases with elevation, and (2) at high elevation, dorsal colouration is under conflicting selection for both crypsis and thermoregulation. By means of standardised photographies of the substratum and colourimetric measurements of lizard dorsal skin, we tested the colour matching between lizard dorsum and background. We found that, along the gradient, lizard dorsal colouration covaried with the colouration of bare soil, but not with other background elements where the lizard is rarely detected. Moreover, supporting our prediction, the degree of crypsis against bare soil decreased with elevation. Hence, our findings suggest local adaptation for crypsis in this lizard along an elevational gradient, but this local adaptation would be hindered at high elevations.

Disentangling the role of heat sources on microhabitat selection of two Neotropical lizard species

Our aim was to disentangle the effects of different heat sources and the non-thermal properties of the substrate in the microhabitat choices of two lizard species living in savanna habitats of central-western Brazil: the teiidAmeivulaaff.ocellifera(N = 43) and the tropiduridTropidurus oreadicus(N = 23). To this end, a mixed structural resource selection function (mixed-SRSF) approach was used, modelling the probability of finding a lizard on a certain microhabitat based on environmental variables of used and simultaneously available places. First, we controlled for the effects of solar radiation, convection and the physical thermal properties of the substrate on substrate temperature. Then we assessed the effects of solar radiation, convection, conduction and the non-thermal properties of the substrate in the probability of use of a certain microhabitat. Results confirmed that substrate temperature was mediated by: air convection > solar radiation > physical thermal properties of the substrates. Moreover, the mixed-SRSF revealed that direct solar radiation and the non-thermal properties of the substrates were the only drivers of microhabitat selection for both species, with approximately the same strength. Our novel approach allowed splitting of the effect of different mechanisms in the microhabitat selection of lizards, which makes it a powerful tool for assessing the conformation of the interactions between different environmental variables mediating animal behaviour.

Aspects of thermal ecology of the meadow lizard (Darevskia praticola)

We studied the thermal biology of the meadow lizard (Darevskia praticola) in the peripheral part of its distribution range (westernmost edge of the distribution area). We assessed whether these lizards actively thermoregulate, estimated the accuracy and effectiveness of thermoregulation, and evaluated the thermal quality of the habitat using the standard thermal parameters: body (), preferred () with set-point range () and operative temperatures (). of the meadow lizard under controlled laboratory conditions was between 27.8°C and 31.4°C. In the field and averaged 29.0°C and 26.1°C, respectively. A large proportion of s fell below the range of the meadow lizard, and lizard s were substantially closer to the species’ range. Obtained values of thermoregulatory indices suggested that the meadow lizard thermoregulated actively, with a rather high accuracy () and effectiveness ( and ), and that their habitat at this locality was thermally favourable during the spring. Our results suggest that thermal requirements of the meadow lizard resemble those of alpine lacertids, while their s and are lower than in most lacertid lizards. Further thermoregulation studies could be an important step in predicting the impact of the global climate change on the meadow lizard and the risks of local extinctions of its peripheral populations.

Exoskeleton may influence the internal body temperatures of Neotropical dung beetles (Col. Scarabaeinae)

The insect exoskeleton is a multifunctional coat with a continuum of mechanical and structural properties constituting the barrier between electromagnetic waves and the internal body parts. This paper examines the ability of beetle exoskeleton to regulate internal body temperature considering its thermal permeability or isolation to simulated solar irradiance and infrared radiation. Seven Neotropical species of dung beetles (Coleoptera, Scarabaeinae) differing in colour, surface sculptures, size, sexual dimorphism, period of activity, guild category and altitudinal distribution were studied. Specimens were repeatedly subjected to heating trials under simulated solar irradiance and infrared radiation using a halogen neodymium bulb light with a balanced daylight spectrum and a ceramic infrared heat emitter. The volume of exoskeleton and its weight per volume unit were significantly more important for the heating rate at the beginning of the heating process than for the asymptotic maximum temperature reached at the end of the trials: larger beetles with relatively thicker exoskeletons heated more slowly. The source of radiation greatly influences the asymptotic temperature reached, but has a negligible effect in determining the rate of heat gain by beetles: they reached higher temperatures under artificial sunlight than under infrared radiation. Interspecific differences were negligible in the heating rate but had a large magnitude effect on the asymptotic temperature, only detectable under simulated sun irradiance. The fact that sun irradiance is differentially absorbed dorsally and transformed into heat among species opens the possibility that differences in dorsal exoskeleton would facilitate the heat gain under restrictive environmental temperatures below the preferred ones. The findings provided by this study support the important role played by the exoskeleton in the heating process of beetles, a cuticle able to act passively in the thermal control of body temperature without implying energetic costs and metabolic changes.

Thermoregulation in the lizard Psammodromus algirus along a 2200-m elevational gradient in Sierra Nevada (Spain)

Achieving optimal body temperature maximizes animal fitness. Since ambient temperature may limit ectotherm thermal performance, it can be constrained in too cold or hot environments. In this sense, elevational gradients encompass contrasting thermal environments. In thermally pauperized elevations, ectotherms may either show adaptations or suboptimal body temperatures. Also, reproductive condition may affect thermal needs. Herein, we examined different thermal ecology and physiology capabilities of the lizard Psammodromus algirus along a 2200-m elevational gradient. We measured field (T(b)) and laboratory-preferred (T(pref)) body temperatures of lizards with different reproductive conditions, as well as ambient (T(a)) and copper-model operative temperature (T(e)), which we used to determine thermal quality of the habitat (d(e)), accuracy (d(b)), and effectiveness of thermoregulation (de-db) indexes. We detected no Tb trend in elevation, while T(a) constrained T(b) only at high elevations. Moreover, while Ta decreased more than 7 °C with elevation, T(pref) dropped only 0.6 °C, although significantly. Notably, low-elevation lizards faced excess temperature (T(e) > T(pref)). Notably, de was best at middle elevations, followed by high elevations, and poorest at low elevations. Nonetheless, regarding microhabitat, high-elevation de was more suitable in sun-exposed microhabitats, which may increase exposition to predators, and at midday, which may limit daily activity. As for gender, d(b) and d(e)-d(b) were better in females than in males. In conclusion, P. algirus seems capable to face a wide thermal range, which probably contributes to its extensive corology and makes it adaptable to climate changes.

Elevational variation in body-temperature response to immune challenge in a lizard

Immunocompetence benefits animal fitness by combating pathogens, but also entails some costs. One of its main components is fever, which in ectotherms involves two main types of costs: energy expenditure and predation risk. Whenever those costs of fever outweigh its benefits, ectotherms are expected not to develop fever, or even to show hypothermia, reducing costs of thermoregulation and diverting the energy saved to other components of the immune system. Environmental thermal quality, and therefore the thermoregulation cost/benefit balance, varies geographically. Hence, we hypothesize that, in alpine habitats, immune-challenged ectotherms should show no thermal response, given that (1) hypothermia would be very costly, as the temporal window for reproduction is extremely small, and (2) fever would have a prohibitive cost, as heat acquisition is limited in such habitat. However, in temperate habitats, immune-challenged ectotherms might show a febrile response, due to lower cost/benefit balance as a consequence of a more suitable thermal environment. We tested this hypothesis in Psammodromus algirus lizards from Sierra Nevada (SE Spain), by testing body temperature preferred by alpine and non-alpine lizards, before and after activating their immune system with a typical innocuous pyrogen. Surprisingly, non-alpine lizards responded to immune challenge by decreasing preferential body-temperature, presumably allowing them to save energy and reduce exposure to predators. On the contrary, as predicted, immune-challenged alpine lizards maintained their body-temperature preferences. These results match with increased costs of no thermoregulation with elevation, due to the reduced window of time for reproduction in alpine environment.

Effect of body mass and melanism on heat balance in Liolaemus lizards of the goetschi clade

Body temperature of ectotherms depends on the environmental temperatures and behavioral adjustments, but morphology may also affect it. For example, in colder environments animals tend to be larger and show higher thermal inertia, as proposed by Bergmann's rule and the heat balance hypothesis (HBH). Additionally, dark coloration increases solar radiation absorption and should accelerate heat gain (Thermal melanism hypothesis, TMH).

We tested Bergmann's rule, HBH and TMH within the Liolaemus goetschi lizards clade that show variability in body size and melanic coloration. We measured heating and cooling rates of live and euthanized animals, and tested how morphology and color affect these rates. Live organisms show less variable and faster heating rates, compared to cooling rates, suggesting behavioral and/ or physiological adjustments.

Our results support Bergmann's rule and the HBH, as larger species show slower heating and cooling rates. However, we did not find a clear pattern to support TMH. The influence of dorsal melanism on heating by radiation was masked by body size effect in live animals, while results from euthanized individuals show no clear effects of melanism on heating rates either. However, when compared three groups of live individuals with different degree of melanism we found that that darker euthanized animals actually heat faster than lighter ones, favoring TMH. Although unresolved aspects remain, body size and coloration influenced heat exchange suggesting complex thermoregulatory strategies in these lizards, probably regulated through physiology and behavior, what may allow these small lizards to inhabit harsh weather environments.

The correlated evolution of biomechanics, gait and foraging mode in lizards

Foraging mode has molded the evolution of many aspects of lizard biology. From a basic sit-and-wait sprinting feeding strategy, several lizard groups have evolved a wide foraging strategy, slowly moving through the environment using their highly developed chemosensory systems to locate prey. We studied locomotor performance, whole-body mechanics and gaits in a phylogenetic array of lizards that use sit-and-wait and wide-foraging strategies to contrast the functional differences associated with the need for speed vs slow continuous movement during foraging. Using multivariate and phylogenetic comparative analyses we tested for patterns of covariation in gaits and locomotor mechanics in relation to foraging mode. Sit-and-wait species used only fast speeds and trotting gaits coupled with running (bouncing) mechanics. Different wide-foraging species independently evolved slower locomotion with walking(vaulting) mechanics coupled with several different walking gaits, some of which have evolved several times. Most wide foragers retain the running mechanics with trotting gaits observed in sit-and-wait lizards, but some wide foragers have evolved very slow (high duty factor) running mechanics. In addition, three evolutionary reversals back to sit-and-wait foraging are coupled with the loss of walking mechanics. These findings provide strong evidence that foraging mode drives the evolution of biomechanics and gaits in lizards and that there are several ways to evolve slower locomotion. In addition, the different gaits used to walk slowly appear to match the ecological and behavioral challenges of the species that use them. Trotting appears to be a functionally stable strategy in lizards not necessarily related to whole-body mechanics or speed.

Colour variation and alternative reproductive strategies in females of the common lizard Lacerta vivipara

Within-sex colour variation is a widespread phenomenon in animals that often plays a role in social selection. In males, colour variation is typically associated with the existence of alternative reproductive strategies. Despite ecological conditions theoretically favourable to the emergence of such alternative strategies in females, the social significance of colour variation in females has less commonly been addressed, relative to the attention given to male strategies. In a population of the common lizard, females display three classes of ventral colouration: pale yellow, orange and mixed. These ventral colours are stable through individual's life and maternally heritable. Females of different ventral colourations displayed different responses of clutch size, clutch hatching success and clutch sex-ratio to several individual and environmental parameters. Such reaction patterns might reflect alternative reproductive strategies in females. Spatial heterogeneity and presence of density- and frequency-dependent feedbacks in the environment could allow for the emergence of such alternative strategies in this population and the maintenance of colour variation in females.

The role of prostaglandins and the hypothalamus in thermoregulation in the lizard, Phrynocephalus przewalskii (Agamidae)

Typically, small lizards rely heavily on behavioral thermoregulation rather than physiological mechanisms to control their rates of warming and cooling. We tested the hypothesis that prostaglandins participate in mediating the cardiovascular response to heating and cooling and temperature regulating neurons in the hypothalamus of the small lizard Phrynocephalus przewalskii. In vivo and in vitro treatments, heart rates (HRs) were all found to be higher during heating than during cooling, hysteresis was distinct below 30 and 26 degrees Celsius, respectively. In vivo, as administration of COX inhibitor, there were no differences in HR between heating and cooling at any body temperature and administration of agonist prostaglandins only produced a significant effect on HR below 25 degrees Celsius. Single-unit activity was recorded extracellularly in vitro with microelectrodes, found the firing rate of the continuous unit increased 23% when the temperature of the artificial cerebrospinal fluid dropped from 30-20 degrees Celsius. We conclude that prostaglandins appear to play only a limited role in modulating heart activity in Phrynocephalus przewalskii and suggest that cold-sensitive neurons in the preoptic and anterior hypothalamus (PO/AH) are involved in thermoregulatory control during heating or cooling.