Thermal ecology of three coexistent desert lizards: Implications for habitat divergence and thermal vulnerability

Altitudinal variation in thermal vulnerability of Qinghai-Tibetan Plateau lizards under climate warming

The survival of ectotherms worldwide is threatened by climate change. Whether increasing temperatures increase the vulnerability of ectotherms inhabiting temperate plateau areas remains unclear. To understand altitudinal variation in the vulnerability of plateau ectotherms to climate warming, Qinghai toad-headed lizards (Phrynocephalus vlangalii) were subjected to semi-natural enclosure experiments with simulated warming at high (2,600 m) and superhigh (3,600 m) elevations of the Dangjin Mountain, China. Our results revealed that the thermoregulatory effectiveness and warming tolerance (WT) of the toad-headed lizards were significantly affected by climate warming at both elevations, but their thermal sensitivity remained unchanged. After warming, the thermoregulatory effectiveness of lizards at superhigh elevations decreased because of the improved environmental thermal quality, whereas that of lizards at high-elevation conditions increased. Although the body temperature selected by high-elevation lizards was also significantly increased, the proportion of their active body temperature falling within the set-point temperature range decreased. This indicates that it is difficult for high-elevation lizards to adjust their body temperatures within a comfortable range under climate warming. Variations in the WT and thermal safety margin (TSM) under climate warming revealed that lizards at the superhigh elevation benefited from improved environmental thermal quality, whereas those at the high elevation originally on the edge of the TSM faced more severe threats and became more vulnerable. Our study highlights the importance of thermal biological traits in evaluating the vulnerability of ectotherms in temperate plateau regions.

Metabolic regulation reduces the oxidative damage of arid lizards in response to moderate heat events

Climate warming poses a significant threat to species worldwide, particularly those inhabiting arid and semi-arid regions where extreme temperatures are increasingly prevalent. However, empirical studies investigating how moderate heat events affect the physiological processes of arid and semi-arid animals are largely scarce. To address this knowledge gap, we used an arid and semi-arid lizard species (Phrynocephalus przewalskii) as a study system. We manipulated thermal environments to simulate moderate heat events (43.5 ± 0.3°C during the heating period) for lizards and examined physiological and biochemical traits related to survival, metabolism, locomotion, oxidative stress, and telomere length. We found that the body condition and survival of the lizards were not significantly affected by moderate heat events, despite an increase in body temperature and a decrease in locomotion at high test temperatures were detected. Mechanistically, we found that the lizards exhibited down-regulated metabolic rates and enhanced activities of antioxidative enzymes, resulting in reduced oxidative damage and stable telomere length under moderate heat events. Based on these findings, which indicated a beneficial regulation of fitness by physiological and biochemical processes, we inferred that moderate heat events did not have a detrimental effect on the toad-headed agama, P. przewalskii. Overall, our research contributes to understanding the impacts of moderate heat events on arid and semi-arid species and highlights the adaptive responses and resilience exhibited by the toad-headed agama in the face of climate warming.

Climate warming has divergent physiological impacts on sympatric lizards

Climate warming is expected to affect the vulnerability of sympatric species differentially due to their divergent traits, but the underlying physiological mechanisms of those impacts are poorly understood. We conducted field warming experiments (present climate vs. warm climate) using open-top chambers to determine the effects of climate warming on active body temperature, oxidative damage, immune competence, growth and survival in two sympatric desert-dwelling lizards, Eremias multiocellata and Eremias argus from May 2019 to September 2020. Our climate warming treatment did not affect survival of the two species, but it did increase active body temperatures and growth rate in E. multiocellata compared to E. argus. Climate warming also induced greater oxidative damage (higher malondialdehyde content and catalase activity) in E. multiocellata, but not in E. argus. Further, climate warming increased immune competence in E. multiocellata, but decreased immune competence in E. argus, with regards to white blood cell counts, bacteria killing ability and relative expression of immunoglobulin M. Our results suggest that climate warming enhances body temperature, and thereby oxidative stress, immune competence and growth in E. multiocellata, but decreases immune competence of E. argus, perhaps as a cost of thermoregulation to maintain body temperatures under climate warming. The divergent physiological effects of climate warming on sympatric species may have profound ecological consequences if it eventually leads to changes in reproductive activities, population dynamics and community structure. Our study highlights the importance of considering interspecific differences in physiological traits when we evaluate the impact of climate warming on organisms, even for those closely-related species coexisting within the same geographical area.

Cool shade and not-so-cool shade: How habitat loss may accelerate thermal stress under current and future climate

Worldwide habitat loss, land-use changes, and climate change threaten biodiversity, and we urgently need models that predict the combined impacts of these threats on organisms. Current models, however, overlook microhabitat diversity within landscapes and so do not accurately inform conservation efforts, particularly for ectotherms. Here, we built and field-parameterized a model to examine the effects of habitat loss and climate change on activity and microhabitat selection by a diurnal desert lizard. Our model predicted that lizards in rock-free areas would reduce summer activity levels (e.g. foraging, basking) and that future warming will gradually decrease summer activity in rocky areas, as even large rocks become thermally stressful. Warmer winters will enable more activity but will require bushes and small rocks as shade retreats. Hence, microhabitats that may seem unimportant today will become important under climate change. Modelling frameworks should consider the microhabitat requirements of organisms to improve conservation outcomes.

Oxidative stress mediates the impact of heatwaves on survival, growth and immune status in a lizard

Climate change often includes increases in the occurrence of extreme environmental events. Among these, heatwaves affect the pace of life and performance of wildlife, particularly ectothermic animals, owing to their low thermoregulatory abilities. However, the underlying mechanisms by which this occurs remain unclear. Evidence shows that heatwaves alter the redox balance of ectotherms, and oxidative stress is a major mediator of life-history trade-offs. Therefore, oxidative stress may mediate the effect of extreme thermal conditions on the life histories of ectotherms. To test this hypothesis, a 2 × 2 experiment was conducted to manipulate the redox balance (through a mitochondrial uncoupler that alleviates oxidative stress) of the desert toad-headed agama (Phrynocephalus przewalskii) exposed to heatwave conditions. We recorded lizard growth and survival rates and quantified their redox and immune statuses. In control lizards (unmanipulated redox balance), heatwave conditions decreased growth and survival and induced oxidative damage and immune responses. By contrast, lizards with alleviated oxidative stress showed close-to-normal growth, survival, and immune status when challenged with heatwaves. These results provide mechanistic insight into the role of oxidative stress in mediating the effects of extreme temperatures on ectothermic vertebrates, which may have major eco-evolutionary implications.

Cataglyphis desert ants use distinct behavioral and physiological adaptations to cope with extreme thermal conditions

Some ant species live in hot and arid environments, such as deserts and savannas. Worker polymorphism-variation in worker size and/or morphology within colonies-is adaptive in such ecosystems because it enhances resistance to heat stress and increases the efficiency of resource exploitation. However, species with small, monomorphic workers are also frequently found in these environments. How species with distinct worker size and degrees of polymorphism deal with such stressful environments remains poorly studied. We investigated the behavioral, physiological, and molecular adaptations that may enhance heat and desiccation tolerance in two sympatric species of Cataglyphis desert ants that differ dramatically in worker size and polymorphism: C. viatica is polymorphic, while C. cubica is small and monomorphic. We found that worker size, water content, water loss, and protein regulation play a key role in thermal resistance. (i) Large C. viatica workers better tolerated heat and desiccation stress than did small C. viatica or C. cubica workers. The former had greater water content and lost proportionally less water to evaporation under thermal stress. (ii) Despite their similar size distribution, workers of C. cubica are more heat tolerant than small C. viatica. This higher degree of tolerance likely stemmed from C. cubica workers having greater relative water content. (iii) Under thermal stress, small C. viatica workers metabolized larger quantities of fat and differentially expressed proteins involved in cellular homeostasis. In contrast, C. cubica downregulated the expression of numerous proteins involved in mitochondrial respiration likely reducing ROS accumulation. (iv) Consistent with these results, large C. viatica workers remained active throughout the day; C. cubica workers displayed a bimodal activity pattern, and small C. viatica remained poorly active outside the nest. Our study shows that ecologically similar ant species with different degrees of worker size polymorphism evolved distinct strategies for coping with extreme heat conditions.

The divergent effects of moderate climate warming on the gut microbiota and energetic state of cold-climate lizards from open and semi-closed microhabitats

Introduction

Understanding the physiological responses to warming temperatures is critical for evaluating the vulnerabilities of animals to climate warming. The physiological responses are increasingly affected by gut microbiota. However, the interactions between physiological responses and the gut microbiota of sympatric animals from various microhabitats in the face of climate change remain largely unknown.

Methods

To evaluate the effects of warming temperatures on animals from different microhabitats, we compared locomotor performance, metabolic rate, growth, survival, and gut microbiota of two sympatric ectothermic species (Eremias argus and Takydromus amurensis) from open and semi-closed microhabitats under present and moderate warming climate conditions, respectively.

Results and discussion

We found that locomotor performance and growth rates of snout-vent length (SVL) were enhanced in both lizard species by warming climate. Interestingly, warming temperatures enhanced resting metabolic rates (RMR) in the open-habitat lizard, E. argus, but depressed them in the semi-closed habitat lizard, T. amurensis. Reversely, the metabolism-related gut microbiota was not affected by warming in E. argus, whereas it was significantly enhanced by warming in T. amurensis, indicating a plausible compensatory effect of the gut microbiota on the metabolic regulation of T. amurensis. Furthermore, warming likely improved immunity in both lizard species by significantly reducing pathogenic bacteria while increasing probiotics. This study found that high-latitude sympatric lizards from both open and semi-closed habitats were beneficial to warming temperatures by physiological modification and regulation of the gut microbiota and highlighted the importance of integrating the physiology and gut microbiota in evaluating the vulnerability of animals to climate warming.

Conserved ecophysiology despite disparate microclimatic conditions in a gecko

Microscale differences in the habitats organisms occupy can influence selection regimes and promote intraspecific variation of traits. Temperature-dependent traits can be locally adapted to climatic conditions or be highly conserved and insensitive to directional selection under all but the most extreme regimes, and thus be similar across populations. The opposing slopes of Nahal Oren canyon in the Carmel Mountains, Israel, are strikingly different: the south-facing slope receives intensive solar radiation, is hot and supports mostly annual vegetation, whereas the north-facing slope is ~10°C cooler, more humid, and supports Mediterranean woodland. We examined whether these differences manifest in the thermal physiology of a common gecko species Ptyodactylus guttatus in controlled laboratory conditions. We predicted that geckos from the hotter south-facing slope would prefer higher temperatures, have faster gut passage times, lower metabolic and evaporative water loss rates, and start diel activity earlier compared with north-facing slope conspecifics. Contrary to these predictions, there were no differences between any of the ecophysiological traits in geckos from the opposing slopes. Nevertheless, our data showed that individuals from the north-facing slope were generally more active in earlier hours of the afternoon compared with south-facing individuals. We suggest that P. guttatus individuals disperse between the slopes and either gene-flow or behavioral plasticity deter local adaptation, resulting in similar physiological traits. Perhaps a stronger contrast in climatic conditions and a stronger barrier are needed to result in interpopulation divergence in temperature-dependent traits.

The Thermal Biology of Takydromus kuehnei Indicates Tropical Lizards From High Elevation Have Not Been Severely Threatened by Climate Change

Climate change poses different threats to animals across latitudes. Tropical species have been proposed to be more vulnerable to climate change. However, the responses of animals from tropical mountains to thermal variation and climate change have been scarcely studied. Here, we investigated the thermal biology traits of a tropical lizard (Takydromus kuehnei) distributed at high elevations (>950 m) and evaluated the vulnerabilities of T. kuehnei by thermal biology traits, thermal safety margin, and thermoregulatory effectiveness. The average active body temperatures of T. kuehnei in the field were 26.28°C and 30.65°C in April and June, respectively. The selected body temperature was 33.23°C, and the optimal temperature for locomotion was 30.60°C. The critical thermal minimum and critical thermal maximum temperatures were 4.79°C and 43.37°C, respectively. Accordingly, the thermal safety margin (1.23°C) and thermoregulatory effectiveness (1.23°C) predicted that T. kuehnei distributed in tropical mountains were not significantly depressed by environmental temperatures. This study implies that high-elevation species in tropical regions may not be severely threatened by ongoing climate change and highlights the importance of thermal biology traits in evaluating the vulnerability of species to climate change.

Vulnerability to global warming of the critically endangered Añelo Sand Dunes Lizard (Liolaemus cuyumhue) from the Monte Desert, Patagonia Argentina

The body temperature of lizards is strongly influenced by the thermal quality of microhabitats, exploiting the favourable environmental temperatures, and avoiding exposure to extreme thermal conditions. For these reasons, reptile populations are considered to be especially vulnerable to changes in environmental temperatures produced by climate change. Here, we study the thermal physiology of the critically endangered Añelo Sand Dunes Lizard (Liolaemus cuyumhue Avila, Morando, Perez and Sites, 2009). We hypothesise that (i) there is a thermal coadaptation between optimal temperature for locomotor performance of L. cuyumhue and its thermal preference; (ii) L. cuyumhue lives in an environment with low thermal quality; and (iii) a rise in environmental temperatures due to global warming will impose a decrement in locomotor speed represented by lower warming tolerance and narrower thermal safety margins, increasing their already high vulnerability. We recorded field body temperatures (T b), preferred body temperatures (T pref), the operative temperature (T e), and the thermal sensitivity of locomotion at different body temperatures. Our results indicate that this lizard is not currently under environmental stress or exceeding its thermal limits, but that it is thermoregulating below T pref to avoid overheating, and that an increase in environmental temperature higher than 3.5 °C will strongly affect the use of microhabitats with direct sun exposure.

Grow fast but don't die young: Maternal effects mediate life-history trade-offs of lizards under climate warming

As postulated by life-history theory, not all life-history traits can be maximized simultaneously. In ectothermic animals, climate warming is predicted to increase growth rates, but at a cost to overall life span. Maternal effects are expected to mediate this life-history trade-off, but such effects have not yet been explicitly elucidated. To understand maternal effects on the life-history responses to climate warming in lizard offspring, we conducted a manipulative field experiment on a desert-dwelling viviparous lacertid lizard Eremias multiocellata, using open-top chambers in a factorial design (maternal warm climate and maternal present climate treatments × offspring warm climate and offspring present climate treatments). We found that the maternal warm climate treatment had little impact on the physiological and life-history traits of adult females (i.e. metabolic rate, reproductive output, growth and survival). However, the offspring warm climate treatment significantly affected offspring growth, and both maternal and offspring warm climate treatments interacted to affect offspring survival. Offspring from the warm climate treatment grew faster than those from the present climate treatment. However, the offspring warm climate treatment significantly decreased the survival rate of offspring from maternal present climate treatment, but not for those from the maternal warm climate treatment. Our study demonstrates that maternal effects mediate the trade-off between growth and survival of offspring lizards, allowing them to grow fast without a concurrent cost of low survival rate (short life span). These findings stress the importance of adaptive maternal effects in buffering the impact of climate warming on organisms, which may help us to accurately predict the vulnerability of populations and species to future warming climates.

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.

Ecophysiology of a lacertid community in the high Moroccan mountains suggests conservation guidelines

Lizard species may differ in their ecophysiology due to adaptation, plasticity and/or phylogeny. In restrictive environments, ecophysiological differences of species living in sympatry are expected to reveal long-term evolutionary responses to the abiotic environment while competitive interactions should be limited. These influences can be disentangled by combining field monitoring with experimental tests. Here, three lacertid lizard species, Atlantolacerta andreanskyi, Scelarcis perspicillata and Podarcis vaucheri sharing high mountain habitats in Oukaimeden (High Atlas, Morocco), were studied. In the field, spatiotemporal variation of the thermal and hydric environment used by the lizards was monitored using data-loggers. In the lab, thermal and hydric ecophysiology was estimated through assessments of preferred temperatures (Tp) and water loss (WL) rates. Species differed in microhabitat use and, hence, in their exposure to variations in temperature and humidity. However, they only differed in their WL (A. andreanskyi > S. perspicillata > P. vaucheri) while their Tp were similar. Such partial differences of species in in the fundamental niche, likely derived from their long-term independent phylogenetic trajectories, can be used to predict their responses to climate and habitat shifts in this and other parts of their respective ranges. Results also confirm previous suggestions that, together with thermal physiology, hydric physiology plays a prominent role in the organisation of lizard communities in the temperate region.

Behavioural thermoregulation by the endangered crocodile lizard (Shinisaurus crocodilurus) in captivity

Understanding the factors that may affect behavioural thermoregulation of endangered reptiles is important for their conservation because thermoregulation determines body temperatures and in turn physiological functions of these ectotherms. Here we measured seasonal variation in operative environmental temperature (T_e), body temperature (T_b), and microhabitat use of endangered crocodile lizards (Shinisaurus crocodilurus) from a captive population, within open and shaded enclosures, to understand how they respond to thermally challenging environments. T_e was higher in open enclosures than in shaded enclosures. The T_b of lizards differed between the open and shaded enclosures in summer and autumn, but not in spring. In summer, crocodile lizards stayed in the water to avoid overheating, whereas in autumn, crocodile lizards perched on branches seeking optimal thermal environments. Crocodile lizards showed higher thermoregulatory effectiveness in open enclosures (with low thermal quality) than in shaded enclosures. Our study suggests that the crocodile lizard is capable of behavioural thermoregulation via microhabitat selection, although overall, it is not an effective thermoregulator. Therefore, maintaining diverse thermal environments in natural habitats for behavioural thermoregulation is an essential measure to conserve this endangered species both in the field and captivity.

Thermal biology and locomotor performance in Phymaturus calcogaster: are Patagonian lizards vulnerable to climate change?

Behavioral and physiological traits of ectotherms are especially sensitive to fluctuations of environmental temperature. In particular, niche-specialist lizards are dependent on their physiological plasticity to adjust to changing environmental conditions. Lizards of the genus Phymaturus are viviparous, mainly herbivorous, and inhabit only rock promontories in the steppe environments of Patagonia and the Andes. Herein, we examine the vulnerability of the southernmost Phymaturus species to global warming: the endemic Phymaturus calcogaster, which lives in a mesic environment in eastern Patagonia. We studied body temperatures in the field (T_b ), preferred body temperatures in a thermogradient (T_pref ), the operative (T_e ) and environmental temperatures, and the dependence of running performance on body temperature. P. calcogaster had a mean T_b (27.04°C) and a mean T_e (31.15°C) both lower than their preferred temperature (T_pref = 36.61°C) and the optimal temperature for running performance (T_o = 37.13°C). Lizard activity seems to be restraint during the early afternoon due high environmental temperatures. However, both, the high safety margin and warming tolerance suggest that the expected increase in environmental temperatures due to global warming (IPCC report in 2018) would not threaten, but indeed enhance locomotor performance in this population.

Thermal tolerance in the urban heat island: thermal sensitivity varies ontogenetically and differs between embryos of two sympatric ectotherms

Most studies of thermal tolerance use adults, but early-life stages (e.g. embryos) are often more sensitive to thermal agitation. Studies that examine effects on embryos rarely assess the potential for thermal tolerance to change with ontogeny or how effects differ among sympatric species, and often utilize unrealistic temperature treatments. We used thermal fluctuations from nests within the urban-heat island to determine how thermal tolerance of embryos changes across development and differs among two sympatric lizard species (Anolis sagrei and A. cristatellus). We applied fluctuations that varied in frequency and magnitude at different times during development and measured effects on embryo physiology, egg survival, and hatchling morphology, growth, and survival. Thermal tolerance differed between the species by∼2 °C: embryos of A. sagrei, a lizard that prefers warmer, open-canopy microhabitats, were more robust to thermal stress than embryos of A. cristatellus, which prefers cooler, closed-canopy microhabitats. Moreover, thermal tolerance changed through development; however, the nature of this change differed between the species. For A. cristatellus, thermal tolerance was greatest mid-development. For A. sagrei the relationship was not statistically clear. The greatest effects of thermal stress were on embryo and hatchling survival and embryo physiology. Hatchling morphology and growth were less affected. Inter-specific responses and the timing of stochastic thermal events with respect to development have important effects on egg mortality. Thus, research that integrates ecologically-meaningful thermal treatments, considers multiple life-history stages, and examines interspecific responses will be critical to make robust predictions of the impacts of global change on wildlife.

Unraveling the influences of climate change in Lepidosauria (Reptilia)

In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans and many species have shifted their geographic ranges, seasonal activities, migration patterns, abundances and interactions in response to these changes. Projections of future climate change are uncertain, but the Earth's warming is likely to exceed 4.8 °C by the end of 21th century. The vulnerability of a population, species, group or system due to climate change is a function of impact of the changes on the evaluated system (exposure and sensitivity) and adaptive capacity as a response to this impact, and the relationship between these elements will determine the degree of species vulnerability. Predicting the potential future risks to biodiversity caused by climate change has become an extremely active field of research, and several studies in the last two decades had focused on determining possible impacts of climate change on Lepidosaurians, at a global, regional and local level. Here we conducted a systematic review of published studies in order to seek to what extent the accumulated knowledge currently allow us to identify potential trends or patterns regarding climate change effects on lizards, snakes, amphisbaenians and tuatara. We conducted a literature search among online literature databases/catalogues and recorded 255 studies addressing the influence of climate change on a total of 1918 species among 49 Lepidosaurian's families. The first study addressing this subject is dated 1999. Most of the studies focused on species distribution, followed by thermal biology, reproductive biology, behavior and genetics. We concluded that an integrative approach including most of these characteristics and also bioclimatic and environmental variables, may lead to consistent and truly effective strategies for species conservation, aiming to buffer the climate change effects on this group of reptiles.

A simulated heat wave shortens the telomere length and lifespan of a desert lizard

Understanding how organisms respond to warming contributes important information to the conservation of biodiversity that is threatened by climate warming. Here, we conducted experiments on a desert agama (Phrynocephalus przewalskii) to test the hypothesis that climate warming (an increase in both mean temperature and heat waves) would induce oxidative stress, shortening telomere length, and thereby decreasing survival. Our results demonstrated that one week of exposure to a simulated heat wave significantly shortened telomere length, and decreased the overwinter survival of lizards, but mean temperature increase did not affect the survival of lizards. However, the antioxidant capacity (anti-oxidative enzyme) was not affected by the warming treatments. Therefore, heat waves might have negative impacts on the desert agama, with shortened telomeres likely causing the lifespan of lizards to decrease under climate warming.