Ecological constraints on the evolutionary association between field and preferred temperatures in Tropidurinae lizards

Environmental temperature predicts resting metabolic rates in tropidurinae lizards

Interspecific variation in metabolic rates may be associated with climate, habitat structure, and resource availability. Despite a strong link between ecology and physiology, there is a dearth in the understanding of how the costs of body maintenance change during ecological transitions. We focused on an ecologically diverse group of neotropical lizards (Tropidurinae) to investigate whether and how resting metabolic rate (RMR) evolved under divergent micro- and macrohabitat conditions. Using a phylogenetic framework, we tested whether species from hot and dry habitats had lower RMRs in relation to those from cooler and mesic habitats, and investigated whether microhabitat usage had an effect over body mass-adjusted RMRs. Our results suggest that RMRs are not phylogenetically structured in Tropidurinae. We found no correlation between metabolism, precipitation, and microhabitat usage. Species from warmer habitats had lower RMR compared to those from cooler habitats, supporting a mechanism of negative compensation in metabolic responses to temperature. Ectotherms from warmer habitats can limit energetic demand and expenditure through reduced RMR, whereas those from cooler habitats may sustain activity despite thermal constraints via increased RMR. Our work highlights the role of temperature in shaping metabolic responses in lizards, giving additional support to the notion that physiology and ecological contexts are intertwined.

Native Lizards Living in Brazilian Cities: Effects of Developmental Environments on Thermal Sensitivity and Morpho-Functional Associations of Locomotion

Environmental conditions often affect developmental processes and consequently influence the range of phenotypic variation expressed at population level. Expansion of urban sites poses new challenges for native species, as urbanization usually affects the intensity of solar exposure and shade availability, determining the thermal regimes organisms are exposed to. In this study, we evaluate the effects of different developmental conditions in a Tropidurus lizard commonly found in Brazilian urban sites. After incubating embryos of Tropidurus catalanensis in two different thermal regimes (Developmental Environments [DE]: cold 24°C and warm 30°C), we measured morphological traits in the neonates and quantified locomotor performance in horizontal and vertical surfaces at three temperatures [Test Temperatures (TT) = 24°C, 30°C and 36°C]. Results indicate effects of developmental temperatures on morphological features, expressing functional implications that might be decisive for the viability of T. catalanensis in urbanized areas. Lizards ran similarly on horizontal and vertical surfaces, and isolated analyses did not identify significant effects of DE or TT on the sprint speeds measured. Absolute Vmax (i.e., the maximum sprint speed reached among all TTs) positively correlated with body size (SVL), and neonates from the warm DE (30°C) were larger than those from the cold DE (24°C). Morpho-functional associations of absolute Vmax also involved pelvic girdle width and forelimb, hindlimb, trunk, and tail lengths. Emerging discussions aim to understand how animals cope with abrupt environmental shifts, a likely common challenge in urbanized sites. Our findings add a new dimension to the topic, providing evidence that temperature, an environmental parameter often affected by urbanization, influences the thermal sensitivity of locomotion and the morphological profile of T. catalanensis neonates. Thermal sensitivity of specific developmental processes may influence the ability of these lizards to remain in habitats that change fast, as those suffering rapid urbanization due to city growth.

Ecological constraints to match field and preferred temperatures in lizards Tropidurus catalanensis (Squamata; Tropiduridae)

We compared microhabitat and body temperatures in the field with thermal preferences of Tropidurus catalanensis to investigate if they match or diverge as demonstration respectively of suitability or poor-quality of the thermal environment. As T. catalanensis is subjected to variable thermal conditions along its distribution and may be jeopardized by the climate change, we measured its thermal preferences after exposure to milder (17 °C-27 °C) and warmer (22 °C-32 °C) thermal conditions to evaluate acclimatory responses and tolerances and vulnerabilities to warming. Field body temperatures tended to be similar to minimum preferred body temperatures, and microhabitat and body temperatures in the field were cooler in the remaining comparisons with thermal preferences [preferred (T_pref), set-point range (T_set), minimum preferred (T_{pref_min}) and maximum preferred (T_{pref_max}) body temperatures], suggesting there was a constraint to warming up in nature. The minimum preferred body temperatures may be a threshold separating proper functioning from markedly noxious impacts due to progressive impairment by the cooling. Difficulties to warm and keep suitable body temperatures may jeopardize overall ecophysiological and behavioral processes with implications for maintenance, fitness, and survival. The constraints to warm may impact T. catalanensis differently depending on its body size and its properties of heat conservation (thermal inertia). Smaller and larger T. catalanensis may respectively cool down easier and have difficulties to warm up, being jeopardized by the constraints due to the cold. The warmer preferred body temperatures coupled with the cooler microhabitats and bodies in nature complicate to anticipate how individuals will respond to climate change, but the acclimation to the warmer temperatures led six of them to death, suggesting they had limited tolerance to heat and would be vulnerable to global warming.

Digit identity matters: origin and evolution of sexual dimorphism in the digit lengths of tropidurid lizards

Sexual dimorphism in digit lengths reflects phenotypic evolution mediated by developmental steroids. Differences in the identity of the sexually-dimorphic digit may evolve if the concentrations of sex-steroid receptors in the digit are easily modified and the initial changes have low impact on fitness. Accordingly, sexual dimorphism in digit lengths might initially originate under neutral selective regimes, being subsequently co-opted by embryonic hormonal effects on sensitive traits that are more likely to be targeted by selection. Correlated variation among sexually-dimorphic traits might therefore reflect pleiotropic hormonal modulation during development. Moreover, the identity and trend of the sexually-dimorphic digit might be evolutionarily labile even among closely-related species. We evaluated this model by assessing the identity of sexually-dimorphic digits among 11 Tropiduridae lizard species and inferring evolutionary patterns of sexual dimorphism. Assuming that digit lengths can be used as a proxy for hormonal modulation of steroid-sensitive traits during development, we tested for evolutionary associations among sexual dimorphism of digit lengths, body size and other traits that may be direct targets of sexual selection in the Tropiduridae. Sexual dimorphism in digit lengths is evolutionarily labile in the Tropiduridae, and diversity, instead of conservatism, seems to rule developmental mechanisms underlying the evolution of sexual dimorphism in digit ratios.

Bite performance surfaces of three ecologically divergent Iguanidae lizards: relationships with lower jaw bones

Traits that interact to perform an ecologically relevant function are expected to be under multivariate non-linear selection. Using the lower jaw morphology as a biomechanical model, we test the hypothesis that lower jaw bones of lizards are subjected to stabilizing and correlational selection, associated with mechanical advantage and maximum bite force. We used three closely related tropidurine species that differ in size, head shape and microhabitat: Eurolophosaurus nanuzae, Tropidurus hispidus and Tropidurus semitaeniatus. We predicted a common pattern of correlational selection on bones that are part of in-levers or part of the out-lever of the lower jaw. The predicted pattern was found in E. nanuzae and T. hispidus, but this could not be shown to be statistically significant. For T. semitaeniatus, we found significant disruptive selection on a contrast involving the surangular, and also significant directional selection on linear combinations of traits in all species. The results indicate that the non-linear selection on lower jaw bones does not reflect an optimum to enhance mechanical advantage in all species. Divergent functional demands and specific ecological contexts of species seem relevant in shaping patterns of selection on morphology.

Independent influence of thermoregulatory cost on the lower and upper set-points of a heliothermic lizard

Studies on ectothermic vertebrates generally lead to average indicators of thermal preferences measured in the laboratory, which do not say about responses to natural environmental change and may not inform about individual variation and its triggering mechanisms. We studied whether and how changes in costs of thermoregulation influence the preferred temperature (T_p) of individual lizards and their energetic investment in thermoregulation by exposing specimens to three treatments of increasing costs, recording body temperature (T_b) and distance walked (energetic investment). Moderate costs induced an investment trade-off between energy-investment in thermoregulation and T_b, and highlighted individual variation that decreased with higher costs. Lower average T_p's were observed in the high costs trials as a result of the decreased values of the lower and upper voluntary T_b's. As costs increased, lizards walked a shorter overall distance and accepted lower T_b's, but lizards still engaged in costly thermoregulation. Individual variation resulted in two main thermoregulatory patterns that in certain ecological contexts may have an important role in decision-making and adjusting to temperatures that are far from optimal temperatures for performance and physiological processes.

Thermal ecology and microhabitat use of an arboreal lizard in two different Pantanal wetland phytophysionomies (Brazil)

Temperature is one of the main environmental variables shaping the evolution and biology of terrestrial ectotherms. The Pantanal is the largest continuous wetland in the World. However, a lack of knowlegde still exists on the thermal ecology of terrestrial ectothems from this wetland. In this context, the thermal ecology of the lizard Tropidurus lagunablanca Carvalho, 2016 (Squamata, Tropiduridae) was investigated in the Brazilian Pantanal. The thermal ecology and microhabitat use of lizards from a riparian forest was compared to lizards from a park savanna. At both studied areas, air and body temperatures of lizards did not differ between sexes. Mean T. lagunablanca body temperatures were higher at the savanna compared to the forest, while air temperatures were similar in both habitats. The main substrates were tree trunks, with a frequency of approximately 90% of the observations. Lizards from the savanna used higher perches than those from the forest despite -in average- trees were higher at the forest. Lizard sun and shade exposure was similar for both areas. Lizards from both habitats showed similar strong linear relationships between body and air temperatures. However, lizard behaviour of using tree trunk perches differently under different sunlight situations suggests that these lizards actively thermoregulate. Further research on the thermoregulation abilities of this species, with a null hypotesis and behavioral observations will shed light on lizard thermal biology. Studies on the ecophysiological aspects of these lizards should be a priority to understand how they will react to climate change and which conservation measures will be more effective concerning their preservation.

The impact of posture and basking orientation on thermoregulation in the Sungazer (Smaug giganteus)

Body temperature (T_b) is one of the most influential factors affecting physiological processes in ectothermic animals. Reptiles use behaviours such as shuttling, and postural and orientation adjustments to ensure that T_b remains close to a target. It is thought that target body temperature (T_target) is aligned to the physiological and behavioural thermal optima of the animal. The Sungazer (Smaug giganteus), a Threatened lizard species, is unique amongst the Cordylidae in that lizards inhabit self-excavated burrows in open grasslands, a habitat in which there are few exposed rock basking sites. In this situation, T_bs are likely to be greatly influenced by postural and orientation adjustments during basking. We measured T_bs using modified iButtons, and calculated T_target of free-ranging Sungazers in order to assess the impact of body posture and orientation in the thermoregulation of the species. We used camera traps to record lizard behaviour at burrow entrances and aligned these measures to measures of T_b. T_target was 30 ± 1.4 °C, and T_bs remained within this range for 371 ± 162 min per day. The anterior body-up postures resulted in faster heating and higher T_bs. Lizards heated faster when facing away from the sun and spent proportionally more time in this orientation in the morning when T_bs were lower than T_target. Our findings suggest that their wide behavioural repertoire allows Sungazers to thermoregulate effectively over a broad range of environmental conditions and may thus be able to effectively respond to changing climatic conditions.

Thermal physiology of Amazonian lizards (Reptilia: Squamata)

We summarize thermal-biology data of 69 species of Amazonian lizards, including mode of thermoregulation and field-active body temperatures (Tb). We also provide new data on preferred temperatures (Tpref), voluntary and thermal-tolerance ranges, and thermal-performance curves (TPC's) for 27 species from nine sites in the Brazilian Amazonia. We tested for phylogenetic signal and pairwise correlations among thermal traits. We found that species generally categorized as thermoregulators have the highest mean values for all thermal traits, and broader ranges for Tb, critical thermal maximum (CTmax) and optimal (Topt) temperatures. Species generally categorized as thermoconformers have large ranges for Tpref, critical thermal minimum (CTmin), and minimum voluntary (VTmin) temperatures for performance. Despite these differences, our results show that all thermal characteristics overlap between both groups and suggest that Amazonian lizards do not fit into discrete thermoregulatory categories. The traits are all correlated, with the exceptions of (1) Topt, which does not correlate with CTmax, and (2) CTmin, and correlates only with Topt. Weak phylogenetic signals for Tb, Tpref and VTmin indicate that these characters may be shaped by local environmental conditions and influenced by phylogeny. We found that open-habitat species perform well under present environmental conditions, without experiencing detectable thermal stress from high environmental temperatures induced in lab experiments. For forest-dwelling lizards, we expect warming trends in Amazonia to induce thermal stress, as temperatures surpass the thermal tolerances for these species.

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.

Thermal biology of the spotted snow skink, Niveoscincus ocellatus, along an altitudinal gradient

Body temperatures in ectotherms are strongly affected by their thermal environment. Ectotherms respond to variation in the thermal environment either by modification of behavioural thermoregulation to maintain their optimal body temperature or by shifting their optimal body temperature. In this study, the body temperatures of males of three populations of spotted snow skinks, Niveoscincus ocellatus, living along an altitudinal gradient (low, mid, and high altitude) were studied in the field and laboratory in spring, summer, and autumn, representing the full activity period of this species. The environmental variation across both sites and seasons affected their field active body temperatures. At the low and mid altitude, N. ocellatus had a higher mean body temperature than at the high altitude. Animals achieved their thermal preference at the low and mid altitude sites in all seasons. At the high altitude, however, N. ocellatus struggled to reach its preferred body temperatures, especially in autumn. The lower body temperature at the high-altitude site is likely due to limited thermal opportunity and/or an effect of avoiding the costs associated with increased intensity of basking.

Methods and pitfalls of measuring thermal preference and tolerance in lizards

Understanding methodological and biological sources of bias during the measurement of thermal parameters is essential for the advancement of thermal biology. For more than a century, studies on lizards have deepened our understanding of thermal ecophysiology, employing multiple methods to measure thermal preferences and tolerances. We reviewed 129 articles concerned with measuring preferred body temperature (PBT), voluntary thermal tolerance, and critical temperatures of lizards to offer: a) an overview of the methods used to measure and report these parameters, b) a summary of the methodological and biological factors affecting thermal preference and tolerance, c) recommendations to avoid identified pitfalls, and d) directions for continued progress in our application and understanding of these thermal parameters. We emphasize the need for more methodological and comparative studies. Lastly, we urge researchers to provide more detailed methodological descriptions and suggest ways to make their raw data more informative to increase the utility of thermal biology studies.

Life-history evolution on tropidurinae lizards: influence of lineage, body size and climate

The study of life history variation is central to the evolutionary theory. In many ectothermic lineages, including lizards, life history traits are plastic and relate to several sources of variation including body size, which is both a factor and a life history trait likely to modulate reproductive parameters. Larger species within a lineage, for example tend to be more fecund and have larger clutch size, but clutch size may also be influenced by climate, independently of body size. Thus, the study of climatic effects on lizard fecundity is mandatory on the current scenario of global climatic change. We asked how body and clutch size have responded to climate through time in a group of tropical lizards, the Tropidurinae, and how these two variables relate to each other. We used both traditional and phylogenetic comparative methods. Body and clutch size are variable within Tropidurinae, and both traits are influenced by phylogenetic position. Across the lineage, species which evolved larger size produce more eggs and neither trait is influenced by temperature components. A climatic component of precipitation, however, relates to larger female body size, and therefore seems to exert an indirect relationship on clutch size. This effect of precipitation on body size is likely a correlate of primary production. A decrease in fecundity is expected for Tropidurinae species on continental landmasses, which are predicted to undergo a decrease in summer rainfall.