Ontogenetic and sexual differences of thermal biology and locomotor performance in a lacertid lizard, Eremias multiocellata

Convergent High O2 Affinity but Distinct ATP-Mediated Allosteric Regulation of Hemoglobins in Oviparous and Viviparous Eremias Lizards from the Qinghai-Tibet Plateau

The functional adaptation and underlying molecular mechanisms of hemoglobins (Hbs) have primarily concentrated on mammals and birds, with few reports on reptiles. This study aimed to investigate the convergent and species-specific high-altitude adaptation mechanisms of Hbs in two Eremias lizards from the Qinghai-Tibet Plateau. The Hbs of high-altitude E. argus and E. multiocellata were characterized by significantly high overall and intrinsic Hb-O2 affinity compared to their low-altitude populations. Despite the similarly low Cl- sensitivities, the Hbs of high-altitude E. argus exhibited higher ATP sensitivity and ATP-dependent Bohr effects than that of E. multiocellata, which could facilitate O2 unloading in respiring tissues. Eremias lizards Hbs exhibited similarly low temperature sensitivities and relatively high Bohr effects at lower temperatures, which could help to stably deliver and release O2 to cold extremities at low temperatures. The oxygenation properties of Hbs in high-altitude populations might be attributed to varying ratios of β2/β1 globin and substitutions on the β2-type globin. Notably, the Asn12Ala in lowland E. argus could cause localized destabilization of the E-helix in the tetrameric Hb by elimination of hydrogen bonds, thereby resulting in its lowest O2 affinity. This study provides a valuable reference for the high-altitude adaptation mechanisms of hemoglobins in reptiles.

A Gecko-Inspired Robot with a Flexible Spine Driven by Shape Memory Alloy Springs

The majority of sprawling-posture quadrupedal vertebrates, such as geckos and lizards, adopt a cyclical lateral swing pattern of their trunk that is coordinated with limb movements to provide extraordinary flexibility and mobility. Inspired by the gecko's locomotory gait and posture, a gecko-like robot with a flexible spine driven by shape memory alloy (SMA) springs was proposed in this work. The static parameters of the SMA spring were experimentally measured, and the flexible spine driven by SMA springs can be deflected bidirectionally. A kinematic model of the spine mechanism was established, and the mathematical relationship between the thermodynamic behavior of the SMA springs and spinal deflection was systematically analyzed. When a gecko trots with a lateral swing pattern of its trunk, the body and the spine show a standing wave shape and a single-peak C-type curve, respectively. The lateral spine deflection and trotting gait were combined in a collaborative model of a flexible spine and limbs to describe in detail the specific relationships between leg joint variables and spine deflection angle. Planar motion tests of a prototype robot were also conducted by using four high-speed cameras to record the trajectory of each point of the body, which verified the proposed model. From the acquired results, it was demonstrated that, compared with a rigid body, a robot with a flexible spine has a longer stride length, higher speed, and a greatly reduced turning radius.

Ontogenic differences and sexual dimorphism of the locomotor performance in a nocturnal gecko, Tarentola mauritanica

Locomotion performance in reptiles is deeply associated with habitat use, escape from predators, prey capture, and territory defense. As ectotherms, this trait in lizards is extremely sensitive to body temperature (BT). However, most studies rarely look at locomotion patterns in an ontogenic perspective. The Moorish gecko, Tarentola mauritanica, was used to investigate the possible effects of distinct BTs on the locomotor performance within juveniles and adults. Not surprisingly, adult individuals significantly outperform the juveniles in speed at every BT. Moreover, except in the 30-day-old juveniles, there is a general trend for an increase of speed with BT. The comparison of these speed values with the ones obtained for diurnal lizard species, corroborates the premise that because nocturnal species are subject to low thermal heterogeneity, little selection for behavioral thermoregulation, but strong selection for high performance at relatively cool temperatures are expected. Furthermore, the higher locomotor performance in adults at 29°C, roughly coincides with previously obtained preferred BTs. However, further studies need to be conducted to build the full performance curve, and to validate the existence of coadaption between behavioral thermoregulation and thermal sensitivity of physiological performance. Finally, this study has found that adult males run significantly faster than females at the highest BTs, highlighting the importance in understanding sex differences, and its potential to drive sex-specific behaviors, ecology, and ultimately fitness.

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

How ectotherms exploit thermal resources has important implications for their habitat utilization and thermal vulnerability to climate warming. To address this issue, we investigated thermal relations of three sympatric lizard species (Eremias argus, Eremias multiocellata, and Phrynocephalus przewalskii) in the desert steppe of Inner Mongolia, China. We determined the thermoregulatory behavior, body temperature (T _b), operative temperature (T _e), selected body temperature (T _sel), and critical thermal maximum (CT_max) of adult lizards. Based on these physiological parameters, we quantified the accuracy and effectiveness of thermoregulation as well as thermal-safety margin for these species. The three species were accurate and effective thermoregulators. The P. przewalskii preferred open habitats, and had a higher T _b than the two Eremias lizards, which preferred shade habitats and shuttled more frequently between the shade and sun. This indicated that the three sympatric lizards have different thermoregulatory behavior and thermal physiology, which might facilitate their coexistence in the desert steppe ecosystem. In addition, the P. przewalskii had higher T _sel and CT_max, and a wider thermal-safety margin than the two Eremias lizards, suggesting that the two Eremias lizards would be more vulnerable to climate warming than P. przewalskii.

Sexual differences in behavioral thermoregulation of the lizard Scelarcis perspicillata

Temperature determines all aspects of the biology of ectotherms. Although sexual differences in thermal ecology are not the rule in lizards, some species exhibit such differences. We studied the effect of sex and reproductive condition on the thermoregulation of an introduced population of Scelarcis perspicillata during the summer in Menorca (Balearic Islands, Spain). These lizards live in the wall surfaces of a limestone quarry, where the sun is scarce because of the narrowness of the quarry walls. The population is sexually dimorphic, with larger males than females. We measured body temperature (T_b) of adult males and females in the field, and air (T_a) and substrate temperature (T_s) at the capture sites, and recorded exposure to sunlight, height of the perch, and type of substrate. We also recorded operative temperatures (T_e) as a null hypothesis of thermoregulation. Finally, we studied the thermal preferences of adult males and females in a laboratory thermal gradient. Thermal preferences were similar for pregnant and non-pregnant females, and sex did not affect the thermal preferences of lizards, even after controlling for the effect of body size. However, in the field, females achieved higher T_b than males, and occupied microhabitats with higher T_a and T_s and lower perch heights than males. Furthermore, females selected perches in full sun at a higher frequency than males. As a consequence, females achieved a higher accuracy and effectiveness of thermoregulation (0.89) than males (0.84). Thus, all else being equal, females would achieve a higher performance than males. The observed results are attributable to sexual differences in behaviour, probably in relation with the reproductive season.

Do sex, body size and reproductive condition influence the thermal preferences of a large lizard? A study in Tupinambis merianae

Body temperature is a key factor in physiological processes, influencing lizard performances; and life history traits are expected to generate variability of thermal preferences in different individuals. Gender, body size and reproductive condition may impose specific requirements on preferred body temperatures. If these three factors have different physiological functions and thermal requirements, then the preferred temperature may represent a compromise that optimizes these physiological functions. Therefore, the body temperatures that lizards select in a controlled environment may reflect a temperature that maximizes their physiological needs. The tegu lizard Tupinambis merianae is one of the largest lizards in South America and has wide ontogenetic variation in body size and sexual dimorphism. In the present study we evaluate intraspecific variability of thermal preferences of T. merianae. We determined the selected body temperature and the rate at which males and females attain their selected temperature, in relation to body size and reproductive condition. We also compared the behavior in the thermal gradient between males and females and between reproductive condition of individuals. Our study show that T. merianae selected body temperature within a narrow range of temperatures variation in the laboratory thermal gradient, with 36.24±1.49°C being the preferred temperature. We observed no significant differences between sex, body size and reproductive condition in thermal preferences. Accordingly, we suggest that the evaluated categories of T. merianae have similar thermal requirements. Males showed higher rates to obtain heat than females and reproductive females, higher rates than non-reproductive ones females. Moreover, males and reproductive females showed a more dynamic behavior in the thermal gradient. Therefore, even though they achieve the same selected temperature, they do it differentially.

Live Fast, Die Young: Experimental Evidence of Population Extinction Risk due to Climate Change

Evidence has accumulated in recent decades on the drastic impact of climate change on biodiversity. Warming temperatures have induced changes in species physiology, phenology, and have decreased body size. Such modifications can impact population dynamics and could lead to changes in life cycle and demography. More specifically, conceptual frameworks predict that global warming will severely threaten tropical ectotherms while temperate ectotherms should resist or even benefit from higher temperatures. However, experimental studies measuring the impacts of future warming trends on temperate ectotherms' life cycle and population persistence are lacking. Here we investigate the impacts of future climates on a model vertebrate ectotherm species using a large-scale warming experiment. We manipulated climatic conditions in 18 seminatural populations over two years to obtain a present climate treatment and a warm climate treatment matching IPCC predictions for future climate. Warmer temperatures caused a faster body growth, an earlier reproductive onset, and an increased voltinism, leading to a highly accelerated life cycle but also to a decrease in adult survival. A matrix population model predicts that warm climate populations in our experiment should go extinct in around 20 y. Comparing our experimental climatic conditions to conditions encountered by populations across Europe, we suggest that warming climates should threaten a significant number of populations at the southern range of the distribution. Our findings stress the importance of experimental approaches on the entire life cycle to more accurately predict population and species persistence in future climates.

Warmer climates accelerate the pace of life of lizards and this demographic change leads to a strong decrease in population growth rate that may ultimately result in population extinctions.

Ongoing climate change has potentially drastic impacts on biodiversity. Because their body temperature depends on their external environment, ectotherm (“cold-blooded”) species are thought to be more at risk from warming climates than endotherm (“warm-blooded”) species that regulate their temperature internally. Tropical ectotherms should be particularly threatened by climate change, while temperate ectotherms should resist or even benefit from higher temperatures. While most of the evidence on the impacts of climate change comes from long-term field studies, experimental evidence of the impact of future climatic conditions is still lacking. Here we investigate the impacts of future climates on a temperate lizard using a seminatural warming experiment. We find that warmer temperatures led to a highly accelerated life cycle and a decrease in adult survival. As a result, we postulate that populations in such warm climates would be expected to go extinct in around 20 y. Comparing our experimental conditions to climatic conditions in European populations of common lizards, we show that many populations should be threatened in the next century, particularly in Southern Europe. Our findings challenge the optimistic view that climate change is only a threat for tropical ectotherms and stress the importance of experimental approaches to predicting the consequences of future warming trends.

Age-related habitat selection by brown forest skinks (Sphenomorphus indicus)

In reptiles, habitat selection is the process whereby suitable habitat is selected that optimizes physiological functions and behavioral performance. Here, we used the brown forest skink (Sphenomorphus indicus) as a model animal and examined whether the frequency of active individuals, environmental temperature, illumination of activity area, and habitat type vary with different age classes. We surveyed the number of active individuals and measured environmental variables at Baiyunshan Mountain in Lishui, Zhejiang, China. We found no difference in the activity frequency of adult and juvenile S. indicus; the activity pattern of active individuals was bimodal. The mean environmental temperature selected by adults was higher than that selected by juveniles. The environmental temperature of active areas measured at 0900-1000 h and 1100-1200 h was higher than at 1400-1500 h; illumination of the active area at 1000-1200 h was also higher than at 1400 h-1600 h. The number of active individuals, the environmental temperature and illumination of activity areas showed pairwise positive correlation. There was a difference in habitat type between juveniles and adults whereby juveniles prefer rock habitats. We predict that active S. indicus select optimal habitats with different environmental temperatures and types to reach the physiological needs particular to their age classes.