Running in cold weather: morphology, thermal biology, and performance in the southernmost lizard clade in the world (Liolaemus lineomaculatus section: Liolaemini: Iguania)

Tracing evolutionary trajectories in the presence of gene flow in South American temperate lizards (Squamata: Liolaemus kingii group)

Evolutionary processes behind lineage divergence often involve multidimensional differentiation. However, in the context of recent divergences, the signals exhibited by each dimension may not converge. In such scenarios, incomplete lineage sorting, gene flow, and scarce phenotypic differentiation are pervasive. Here, we integrated genomic (RAD loci of 90 individuals), phenotypic (linear and geometric traits of 823 and 411 individuals, respectively), spatial, and climatic data to reconstruct the evolutionary history of a speciation continuum of liolaemid lizards (Liolaemus kingii group). Specifically, we (a) inferred the population structure of the group and contrasted it with the phenotypic variability; (b) assessed the role of postdivergence gene flow in shaping phylogeographic and phenotypic patterns; and (c) explored ecogeographic drivers of diversification across time and space. We inferred eight genomic clusters exhibiting leaky genetic borders coincident with geographic transitions. We also found evidence of postdivergence gene flow resulting in transgressive phenotypic evolution in one species. Predicted ancestral niches unveiled suitable areas in southern and eastern Patagonia during glacial and interglacial periods. Our study underscores integrating different data and model-based approaches to determine the underlying causes of diversification, a challenge faced in the study of recently diverged groups. We also highlight Liolaemus as a model system for phylogeographic and broader evolutionary studies.

Does heat tolerance actually predict animals' geographic thermal limits?

The "climate extremes hypothesis" is a major assumption of geographic studies of heat tolerance and climatic vulnerability. However, this assumption remains vastly untested across taxa, and multiple factors may contribute to uncoupling heat tolerance estimates and geographic limits. Our dataset includes 1000 entries of heat tolerance data and maximum temperatures for each species' known geographic limits (hereafter, Tmax). We gathered this information across major animal taxa, including marine fish, terrestrial arthropods, amphibians, non-avian reptiles, birds, and mammals. We first tested if heat tolerance constrains the Tmax of sites where species could be observed. Secondly, we tested if the strength of such restrictions depends on how high Tmax is relative to heat tolerance. Thirdly, we correlated the different estimates of Tmax among them and across species. Restrictions are strong for amphibians, arthropods, and birds but often weak or inconsistent for reptiles and mammals. Marine fish describe a non-linear relationship that contrasts with terrestrial groups. Traditional heat tolerance measures in thermal vulnerability studies, like panting temperatures and the upper set point of preferred temperatures, do not predict Tmax or are inversely correlated to it, respectively. Heat tolerance restricts the geographic warm edges more strongly for species that reach sites with higher Tmax for their heat tolerance. These emerging patterns underline the importance of reliable species' heat tolerance indexes to identify their thermal vulnerability at their warm range edges. Besides, the tight correlations of Tmax estimates across on-land microhabitats support a view of multiple types of thermal challenges simultaneously shaping ranges' warm edges for on-land species. The heterogeneous correlation of Tmax estimates in the ocean supports the view that fish thermoregulation is generally limited, too. We propose new hypotheses to understand thermal restrictions on animal distribution.

Latitudinal pattern of the thermal sensitivity of running speed in the endemic lizard Liolaemus multimaculatus

Physiological performance in lizards may be affected by climate across latitudinal or altitudinal gradients. In the coastal dune barriers in central-eastern Argentina, the annual maximum environmental temperature decreases up to 2°C from low to high latitudes, while the mean relative humidity of the air decreases from 50% to 25%. Liolaemus multimaculatus, a lizard in the family Liolaemidae, is restricted to these coastal dunes. We investigated the locomotor performance of the species at 6 different sites distributed throughout its range in these dune barriers. We inquired whether locomotor performance metrics were sensitive to the thermal regime attributable to latitude. The thermal performance breadth increased from 7% to 82% with latitude, due to a decrease in its critical thermal minimum of up to 5°C at higher latitudes. Lizards from high latitude sites showed a thermal optimum, that is, the body temperature at which maximum speed is achieved, up to 4°C lower than that of lizards from the low latitude. At relatively low temperatures, the maximum running speed of high-latitude individuals was faster than that of low-latitude ones. Thermal parameters of locomotor performance were labile, decreasing as a function of latitude. These results show populations of L. multimaculatus adjust thermal physiology to cope with local climatic variations. This suggests that thermal sensitivity responds to the magnitude of latitudinal fluctuations in environmental temperature.

Thermoregulation of Liolaemus aparicioi (Iguania: Liolaemidae) along a 1000 m elevational gradient in La Paz Valley, La Paz, Bolivia

Lizard species have diverse behavioral and physiological responses to thermo-environmental conditions, which allow them to inhabit a broad range of latitudes and elevations. Because the availability of suitable thermal resources is limited and more variable at high-elevation environments than at lower elevations, we expect high-elevation lizards to be constrained in their thermoregulation relative to lizards at lower elevations by the fewer available thermal resources to reach optimal temperatures (colder environment). We studied the thermal biology of an endemic and Critically Endangered lizard, Liolaemus aparicioi, to assess its thermal responses along a 1000 m elevational gradient in La Paz Valley from May to August of 2015 (dry season). We took field body and microhabitat temperatures at capture sites (substrate and air above ground), and body size (snout-vent length and mass) of individuals at Taypichullo (3000 m asl), Gran Jardín de la Revolución Municipal Park (3500 m asl), and Taucachi (4000 m asl) localities. Operative temperatures were taken from calibrated models deployed in different available microhabitats. Preferred temperatures and thermal tolerance limits were determined in laboratory settings for lizards from each locality. Field body, microhabitat, and operative temperatures decreased with increasing elevation and differed between sexes. Lizards at the high elevation locality had the lowest thermoregulatory efficiency as compared with the mid and lower elevation localities. In laboratory measurements, while the preferred temperatures varied between sexes, pooled preferred temperatures and thermal tolerances were similar in all localities. Although thermal resources at high elevation can limit thermoregulatory possibilities in L. aparicioi, behavioral microhabitat use, time allocated to thermoregulation, and physiological adjustments seem to be possible strategies to counteract thermal costs along elevational gradients.

Looking at the past to infer into the future: Thermal traits track environmental change in Liolaemidae

The diversity of habitats generated by the Andes uplift resulted a mosaic of heterogeneous environments in South America for species to evolve a variety of ecological and physiological specializations. Species in the lizard family Liolaemidae occupy a myriad of habitats in the Andes. Here, we analyze the tempo and mode of evolution in the thermal biology of liolaemids. We assessed whether there is evidence of local adaptation (lability) or conservatism (stasis) in thermal traits. We tested the hypothesis that abiotic factors (e.g., geography, climate) rather than intrinsic factors (egg-laying [oviparous] or live-bearing [viviparous], substrate affinity) explain variation in field active body temperature (T_b ), preferred temperature (T_p ), hours of restriction of activity, and potential hours of activity. Although most traits exhibited high phylogenetic signal, we found variation in thermal biology was shaped by geography, climate, and ecological diversity. Ancestral character reconstruction showed shifts in T_b tracked environmental change in the past ∼20,000 years. Thermal preference is 3°C higher than T_b , yet exhibited a lower rate of evolution than T_b and air temperature. Viviparous Liolaemus have lower T_b s than oviparous species, whereas T_p is high for both modes of reproduction, a key difference that results in a thermal buffer for viviparous species to cope with global warming. The rapid increase in environmental temperatures expected in the next 50-80 years in combination with anthropogenic loss of habitats are projected to cause extirpations and extinctions in oviparous species.

Comparative thermal ecophysiology in Pristidactylus scapulatus populations from the Puna region of Argentina

Reptiles are important models for understanding fundamental aspects of physiological ecology and for assessing how environmental change can impact biodiversity. Abiotic factors (micro-environmental temperatures, operative temperatures, thermal quality) may vary geographically along an altitudinal and latitudinal gradient, and therefore the different thermal resources available for thermoregulation also vary. Comparative analyses among populations provide an opportunity to understand how variation in abiotic factors can affect different ecophysiological traits of a species at different geographical points. Our objective was to carry out a comparative study between two populations of Pristidactylus scapulatus in the Puna region of Argentina, providing the first data available on thermal ecophysiology, thermoregulatory efficiency and locomotor performance of the species. We determined field body temperature, micro-environmental temperatures and operative temperatures. In the laboratory, we measured preferred temperatures and calculated the index of thermoregulatory efficiency. In addition, we recorded critical temperature (minimum and maximum) and we estimated the thermal sensitivity of locomotion by measuring sprint speed at different body temperatures; based on these data we calculated the optimal temperature for performance, the optimal performance breadth and thermal safety margin. Air temperatures and operative temperatures were different between sites. However, we only found differences between populations in the minimum critical temperatures, with these being lower at higher latitude. We note that P. scapulatus populations adjust optimal temperatures of performance to field body temperatures and preferred temperatures, which could reduce the costs of thermoregulation in lizards with limited daily activity and who inhabit sites with variable and unpredictable environment temperatures. We conclude that Pristidactylus scapulatus has thermal sensitivity in locomotor performance, is a moderate thermoregulator with respect to the environment and is a eurithermic lizard, which has thermal flexibility in the cold.

Stagewise resolution of temperature-dependent embryonic and postembryonic development in the cowpea seed beetle Callosobruchus maculatus (F.)

BACKGROUND

The thermal plasticity of life-history traits receives wide attention in the recent biological literature. Of all the temperature-dependent traits studied, developmental rates of ectotherms are especially often addressed, and yet surprisingly little is known about embryonic responses to temperature, including changes in the thermal thresholds and thermal sensitivity during early development. Even postembryonic development of many cryptically living species is understood superficially at best.

RESULTS

This study is the first to estimate the exact durations of developmental stages in the cowpea seed beetle C. maculatus from oviposition to adult emergence at five permissive constant temperatures from 20 to 32 °C. Early embryonic development was tracked and documented by means of destructive sampling and subsequent confocal imaging of fluorescently stained specimens. Late embryonic and early larval development was studied with the use of destructive sampling and light microscopy. Well-resolved temporal series based on thousands of embryos allowed precise timing of the following developmental events: formation of the blastoderm; formation, elongation, and retraction of the germ band; dorsal closure; the onset and completion of sclerotization of the cuticle; hatching, and penetration of the first-instar larva into the cowpea seed. Pupation and adult eclosion were observed directly through an incision in the seed coat. The thermal phenotype of C. maculatus was found to vary in the course of ontogeny and different stages scaled disproportionately with temperature, but pitfalls and caveats associated with analyses of relative durations of individual stages are also briefly discussed.

CONCLUSION

Disproportionate changes in developmental durations with temperature may have important implications when study design requires a high degree of synchronization among experimental embryos or when the occurrence of particular stages in the field is of interest, as well as in any other cases when development times need to be estimated with precision. This work provides one of the first examples of integration of embryological techniques with ecophysiological concepts and will hopefully motivate similar projects in the future. While experiments with Drosophila continue to be the main source of information on animal development, knowledge on other model species is instrumental to building a broader picture of developmental phenomena.

Running performance with emphasis on low temperatures in a Patagonian lizard, Liolaemus lineomaculatus

Lizard activity and endurance of cold climate is regulated by several factors such as evolutionary potential, acclimatization capacity, physiological tolerance, and locomotion among thermally advantageous microenvironments. Liolaemus lineomaculatus, a lizard inhabiting a wide range of cold environments in Patagonia, provides an excellent model to test interpopulation variability in thermal performance curves (TPCs) and usage of microhabitats. We obtained critical thermal minima and maxima, and performed running trials at eight temperatures using lizards from both a temperate-site (high-altitude) population at 42° S and a cold-site population at 50° S. The availability of environmental temperatures for running performance in open ground and in potential lizard refuges were recorded, and showed that lizards in the temperate site had a greater availability of thermal environments offering temperatures conducive to locomotion. Generalized additive mixed models showed that the two populations displayed TPCs of different shapes in 0.15 m runs at temperatures near their optimal temperature, indicating a difference in thermal sensitivity at high temperatures. However, the rest of the locomotor parameters remained similar between Liolaemus lineomaculatus from thermal and ecological extremes of their geographic distribution and this may partly explain their ability to endure a cold climate.

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.

Potential benefits from global warming to the thermal biology and locomotor performance of an endangered Patagonian lizard

Global warming can significantly affect many aspects of the biology of animal species, including their thermal physiology and physiological performance. Thermal performance curves provide a heuristic model to evaluate the impacts of temperature on the ecophysiology of ectotherms. When integrated with other thermal biology parameters, they can be used to predict the impacts of climate change on individual fitness and population viability. In this study, we combine holistic measures of thermal physiology and the thermal sensitivity of locomotor performance with environmental temperatures measured at fine scale to estimate the vulnerability to global warming of the endangered Patagonian lizard Phymaturus tenebrosus. Our results indicate that this lizard exhibits its preferred temperatures and maximum locomotor performance at higher temperatures than the mean temperature it currently experiences in its habitat. In addition, it exhibits a low effectiveness of thermoregulation, being a poor thermoregulator. In view of the results obtained, we suggest that the climatic conditions of Patagonia may be advantageous for P. tenebrosus to survive future global warming, since its thermal physiology and locomotor performance may improve under increasing in environmental temperatures in its habitat.

Effect of temperature on the locomotor performance of species in a lizard assemblage in the Puna region of Argentina

Locomotion is relevant to the ecology of reptiles because of its presumed influence on an organism's Darwinian fitness. Moreover, in ectothermic species, physiological performance capacity is affected by body temperature. We analyzed two components of locomotor performance in three species of lizards, Phymaturus extrilidus, Liolaemus parvus, and Liolaemus ruibali, in the Puna environment of Argentina. First, we estimated the thermal sensitivity of locomotion by measuring sprint speed at four different body temperatures. We included two measures of sprint speed: initial velocity and long sprint for sustained runs. Based on these data, we calculated the optimal temperature for performance and the optimal performance breadth. We also estimated endurance capacity at a single temperature. Maximum sprint speed for L. parvus was greater than L. ruibali and P. extrilidus in both initial velocity and long sprint. In contrast, L. parvus exhibited lower levels of endurance than L. ruibali and P. extrilidus. However, endurance in L. ruibali exceeded that of P. extrilidus. The species differed in the optimal temperature for the initial velocity with the lowest for L. ruibali (31.8 °C) followed by P. extrilidus (33.25 °C) and then L. parvus (36.25 °C). The optimal temperature for long sprint varied between 32 and 36 °C for all species. We found that all species attained maximum performance at body temperatures commonly experienced during daily activity, which was higher than the thermal quality of the environment. We found evidence for thermal sensitivity in locomotor performance in these species. However, we also show that the broad thermal breadth of performance suggests that the lizards are capable of sustaining near optimal levels of locomotor performance at ambient temperatures that would appear to be suboptimal. Thus, this lizard assemblage is capable of coping with the highly variable climatic conditions in the Puna region of Argentina.

Thermal niche evolution across replicated Anolis lizard adaptive radiations

Elucidating how ecological and evolutionary mechanisms interact to produce and maintain biodiversity is a fundamental problem in evolutionary ecology. Here, we focus on how physiological evolution affects performance and species coexistence along the thermal niche axis in replicated radiations of Anolis lizards best known for resource partitioning based on morphological divergence. We find repeated divergence in thermal physiology within these radiations, and that this divergence significantly affects performance within natural thermal environments. Morphologically similar species that co-occur invariably differ in their thermal physiology, providing evidence that physiological divergence facilitates species coexistence within anole communities. Despite repeated divergence, phylogenetic comparative analyses indicate that physiological traits have evolved more slowly than key morphological traits related to the structural niche. Phylogenetic analyses also reveal that physiological divergence is correlated with divergence in broad-scale habitat climatic features commonly used to estimate thermal niche evolution, but that the latter incompletely predicts variation in the former. We provide comprehensive evidence for repeated adaptive evolution of physiological divergence within Anolis adaptive radiations, including the complementary roles of physiological and morphological divergence in promoting community-level diversity. We recommend greater integration of performance-based traits into analyses of climatic niche evolution, as they facilitate a more complete understanding of the phenotypic and ecological consequences of climatic divergence.

How sensitive are temperate tadpoles to climate change? The use of thermal physiology and niche model tools to assess vulnerability

Ectotherms are vulnerable to climate change, given their dependence on temperature, and amphibians are particularly interesting because of their complex life cycle. Tadpoles may regulate their body temperature by using suitable thermal microhabitats. Thus, their physiological responses are the result of adjustment to the local thermal limits experienced in their ponds. We studied three anuran tadpole species present in Argentina and Chile: Pleurodema thaul and Pleurodema bufoninum that are seasonal and have broad geographic ranges, and Batrachyla taeniata, a geographically restricted species with overwintering tadpoles. Species with restricted distribution are more susceptible to climate change than species with broader distribution that may cope with potential climatic changes in the environments in which they occur. We aim to test whether these species can buffer the potential effects of climate warming. We used ecological niche models and the outcomes of their thermal attributes (critical thermal limits, optimal temperature, and locomotor performance breadth) as empirical evidence of their capacity. We found that Pleurodema species show broader performance curves, related to their occurrence, while the geographically restricted B. taeniata shows a narrower thermal breadth, but is faster in warmer conditions. The modeled distributions and empirical physiological results suggest no severe threats for these three anurans. However, the risk level is increasing and a retraction of their distribution range might be possible for Pleurodema species, and some local population extinctions may happen, particularly for the narrowly distributed B. taeniata.

Evolution of the cloacal and genital musculature, and the genitalia morphology in liolemid lizards (Iguania: Liolaemidae) with remarks on their phylogenetic bearing

In this study, we describe the intra- and interspecific anatomical variations of cloacal and related muscles of male and female genitalia in species of five iguanian genera (three liolemid:Ctenoblepharys,Liolaemus, andPhymaturusplusDiplolaemusleopardinusandTropidurusmelanopleurusas outgroups). We found variations (seventeen characters) in topology, origin and insertion areas, tendon morphology and size of the musculature of this region. We also describe the variations of hemipeneal morphology, which is especially notable for the hemipenis ofC. adspersa,D. leopardinus, andT. melanopleurus, as this is first time they are described in the literature. Among the most significant findings are the identification of three new muscles, two of them inserted on the roof of the cloacal chamber (anterior and posterior cloacal retractor) and the third inserted superficially in the floor of the cloaca, just before anterior to the precloacal glands row (superficialis cloacalis retractor). We report sexual dimorphism in seven muscle characters. Musculature related to hemiclitoris is reduced in proportion to its size in comparison to the degree of development of male genitalia and associated musculature. The evolution of characters was traced on the known phylogenetic hypotheses of relationships among families. Characters taken from the cloacal/genital myology bring similar support to the liolaemid tree even rooting the analysis using different outgroups. In addition, a phylogenetic study using only myological characters was performed. In this case,C. adspersawas found to be more related toLiolaemusspecies instead of being basal toLiolaemusplusPhymaturus.

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.

Thermoregulatory performance and habitat selection of the eastern box turtle (Terrapene carolina carolina)

Environmental conditions may affect individual physiological processes that influence short-term performance and ultimately growth, survival and reproduction. As such, habitats selected by animals must provide suitable and adequate resources. Ectothermic species are highly dependent on climatic conditions and ambient temperatures that dictate body temperature regulation and in turn physiological processes. We investigated the thermoregulatory performance, habitat selection, and movements of an ectothermic vertebrate, the Eastern box turtle (Terrapene carolina carolina) to assess the importance of thermoregulatory physiology in habitat selection. We evaluated the relationship between habitat selection and thermoregulatory performance in Southwest Ohio over two active seasons from May until October. We found that T. carolina selected shaded habitats, including evergreen and deciduous forests, as well as herbaceous grasslands, conformed to the ambient temperatures throughout the active season, although these habitats had temperatures below those expected based on thermal optima of box turtles. Further, we found that movement was not correlated with internal body temperature. Our study shows that thermal conditions are not paramount in habitat selection of box turtles, but that cooler temperatures do not have an effect on the extent of their locomotion.

Thermoregulatory Behavior Simultaneously Promotes and Forestalls Evolution in a Tropical Lizard

The role of behavior in evolution has long been discussed, with some arguing that behavior promotes evolution by exposing organisms to selection (behavioral drive) and others proposing that it inhibits evolution by shielding organisms from environmental variation (behavioral inertia). However, this discussion has generally focused on the effects of behavior along a single axis without considering that behavior simultaneously influences selection in various niche dimensions. By examining evolutionary change along two distinct niche axes-structural and thermal-we propose that behavior simultaneously drives and impedes evolution in a group of Anolis lizards from the Caribbean island of Hispaniola. Specifically, a behavioral shift in microhabitat to boulders at high altitude enables thermoregulation, thus forestalling physiological evolution in spite of colder environments. This same behavioral shift drives skull and limb evolution to boulder use. Our results emphasize the multidimensional effects of behavior in evolution. These findings reveal how, rather than being diametrically opposed, niche conservatism and niche lability can occur simultaneously. Furthermore, patterns of niche evolution may vary at different geographic scales: because of thermoregulatory behavior, lizards at high and low elevation share similar microclimatic niches (consistent with niche conservatism) while inhabiting distinct macroclimatic environments (consistent with niche divergence). Together, our results suggest that behavior can connect patterns of niche divergence and conservatism at different geographic scales and among traits.

Energy expenditure of the spotted snow skink, Niveoscincus ocellatus, at two climatic extremes of its distribution range

The study of energy expenditure between populations of a wide ranging ectothermic species may provide an insight into how organisms respond to variation in environmental conditions. In this study, the energy expenditure of male spotted snow skinks, Niveoscincus ocellatus, living at the two extremes of the species' distribution range (warm lowland versus cold alpine site) was measured using the doubly labelled water method. Males at the cold alpine site expended more energy per gram per hour compared to their counterparts living at the warm lowland site. Lizards living at high altitude were active at lower temperatures compared with those at the low altitude site, which resulted in a longer activity time for the highland population. However, the differences in energy expenditure cannot be explained only by these differences in activity time. We further suggest that at the cold alpine site, lizards compensated for the low temperatures by elevating their metabolism which subsequently increased their energy expenditure. An elevated metabolic rate combined with modified thermoregulatory behaviour is likely an important mechanism allowing N. ocellatus to cope with the cold environments at high altitude sites.

Thermal sensitivity of cold climate lizards and the importance of distributional ranges

One of the fundamental goals in macroecology is to understand the relationship among species' geographic ranges, ecophysiology, and climate; however, the mechanisms underlying the distributional geographic patterns observed remain unknown for most organisms. In the case of ectotherms this is particularly important because the knowledge of these interactions may provide a robust framework for predicting the potential consequences of climate change in these organisms. Here we studied the relationship of thermal sensitivity and thermal tolerance in Patagonian lizards and their geographic ranges, proposing that species with wider distributions have broader plasticity and thermal tolerance. We predicted that lizard thermal physiology is related to the thermal characteristics of the environment. We also explored the presence of trade-offs of some thermal traits and evaluated the potential effects of a predicted scenario of climate change for these species. We examined sixteen species of Liolaemini lizards from Patagonia representing species with different geographic range sizes. We obtained thermal tolerance data and performance curves for each species in laboratory trials. We found evidence supporting the idea that higher physiological plasticity allows species to achieve broader distribution ranges compared to species with restricted distributions. We also found a trade-off between broad levels of plasticity and higher optimum temperatures of performance. Finally, results from contrasting performance curves against the highest environmental temperatures that lizards may face in a future scenario (year 2080) suggest that the activity of species occurring at high latitudes may be unaffected by predicted climatic changes.

Effects of different substrates on the sprint performance of lizards

The variation in substrate structure is one of the most important determinants of the locomotor abilities of lizards. Lizards are found across a range of habitats, from large rocks to loose sand, each of them with conflicting mechanical demands on locomotion. We examined the relationships among sprint speed, morphology and different types of substrate surfaces in species of lizards that exploit different structural habitats (arboreal, saxicolous, terrestrial and arenicolous) in a phylogenetic context. Our main goals were to assess which processes drive variability in morphology (i.e. phylogeny or adaptation to habitat) in order to understand how substrate structure affects sprint speed in species occupying different habitats and to determine the relationship between morphology and performance. Liolaemini lizards show that most morphological traits are constrained by phylogeny, particularly toe 3, the femur and foot. All ecological groups showed significant differences on rocky surfaces. Surprisingly, no ecological group performed better on the surface resembling its own habitat. Moreover, all groups exhibited significant differences in sprint speed among the three different types of experimental substrates and showed the best performance on sand, with the exception of the arboreal group. Despite the fact that species use different types of habitats, the highly conservative morphology of Liolaemini species and the similar levels of performance on different types of substrates suggest that they confer to the ‘jack of all trades and master of none’ principle.