Would behavioral thermoregulation enable pregnant viviparous tropical lizards to cope with a warmer world?

Cooling down is as important as warming up for a large-bodied tropical reptile

An ectotherm's performance and physiological function are strongly tied to environmental temperature, and many ectotherms thermoregulate behaviourally to reach optimum body temperatures. Tropical ectotherms are already living in environments matching their thermal tolerance range and may be expected to conform to environmental temperatures. We tracked the body temperatures (Tb) of 163 estuarine crocodiles across 13 years and compared Tb of 39 crocodiles to water temperature gathered using fish-borne sensors (Tw) across 3 years (2015-2018). While Tb largely conformed closely to Tw, we found inter- and intra-individual differences in relative body temperature (Tb-Tw) that depended on sex and body size as well as the time of day and year. Deviations from Tw, especially during the warm parts of the year, suggest that thermoregulatory behaviour was taking place: we found patterns of warming and cooling events that seemed to mediate this variation in Tb. Thermoregulatory behaviour was observed most frequently in larger individuals, with warming events common during winter and cooling events common during summer. By observing free-ranging animals across multiple years, we found that estuarine crocodiles show yearly patterns of active cooling and warming behaviours that modify their body temperature, highlighting their resilience in the face of recent climate warming. Our work also provides the first evidence for thermal type in large-bodied reptiles.

Coping with drought? The hidden microhabitat selection and underground movements of amphisbaenians under summer drought conditions

Habitat selection is a dynamic process that depends on many environmental variables that can vary with weather conditions. This is important because, within a context of global change, extreme weather events, such as severe droughts, are predicted to become more frequent. We examined the patterns of microhabitat selection and underground movements (using PIT-tag telemetry) of a strictly fossorial reptile, the North African checkboard amphisbaenian Trogonophis wiegmanni, during the summer drought period. We aimed to test whether changes in strategies of habitat use and movements could allow this amphisbaenian to cope with unfavorable weather. We found that during the summer drought period, T. wiegmanni did not use the microhabitats in relationship to their availability, but particularly selected sites with high abundance of rocks but also areas under a high cover of bushes, where environmental conditions were more favorable. We also found, using PIT-tag telemetry, that the numbers of T. wiegmanni individuals located under rocks and their activity (number of days with movements) decreased largely in summer. However, the animals were not entirely inactive, but, especially males were active below the ground under bushes and made some relatively long underground hidden movements between favorable areas.

Flexibility in thermal requirements: a comparative analysis of the wide-spread lizard genus Sceloporus

Adaptation or acclimation of thermal requirements to environmental conditions can reduce thermoregulation costs and increase fitness, especially in ectotherms, which rely heavily on environmental temperatures for thermoregulation. Insight into how thermal niches have shaped thermal requirements across evolutionary history may help predict the survival of species during climate change. The lizard genus Sceloporus has a widespread distribution and inhabits an ample variety of habitats. We evaluated the effects of geographical gradients (i.e. elevation and latitude) and local environmental temperatures on thermal requirements (i.e. preferred body temperature, active body temperature in the field, and critical thermal limits) of Sceloporus species using published and field-collected data and performing phylogenetic comparative analyses. To contrast macro- and micro-evolutional patterns, we also performed intra-specific analyses when sufficient reports existed for a species. We found that preferred body temperature increased with elevation, whereas body temperature in the field decreased with elevation and increased with local environmental temperatures. Critical thermal limits were not related to the geographic gradient or environmental temperatures. The apparent lack of relation of thermal requirements to geographic gradient may increase vulnerability to extinction due to climate change. However, local and temporal variations in thermal landscape determine thermoregulation opportunities and may not be well represented by geographic gradient and mean environmental temperatures. Results showed that Sceloporus lizards are excellent thermoregulators, have wide thermal tolerance ranges, and the preferred temperature was labile. Our results suggest that Sceloporus lizards can adjust to different thermal landscapes, highlighting opportunities for continuous survival in changing thermal environments.

Behavioral Thermoregulation by Mothers Protects Offspring from Global Warming but at a Cost

AbstractThermal conditions during embryonic development affect offspring phenotype in ectotherms. Therefore, rising environmental temperatures can have important consequences for an individual's fitness. Nonetheless, females have some capacity to compensate for potential negative consequences that adverse developmental environments may have on their offspring. Recent studies show that oviparous reptiles exhibit behavioral plasticity in nest site selection, which can buffer their embryos against high incubation temperatures; however, much less is known about these responses in viviparous reptiles. We subjected pregnant viviparous skinks, Saiphos equalis, to current or projected midcentury (2050) temperatures to test (i) how elevated temperatures affect female thermoregulatory and foraging behavior; (ii) whether temperatures experienced by females during pregnancy negatively affect the morphology, performance, and behavior of hatchlings; and (iii) whether behavioral thermoregulation during pregnancy is costly to females. Females from the elevated temperature treatment compensated by going deeper belowground to seek cooler temperatures and eating less, and they consequently had a lower body mass relative to snout-to-vent length (condition estimator) compared with females from the current thermal treatment. The temperatures experienced by females in the elevated temperature treatment were high enough to affect foraging and locomotor performance but not the morphology and growth rate of hatchlings. By seeking cooler temperatures, mothers can mitigate some of the effects of high temperatures on their offspring (e.g., reduced body size and growth). However, this protective behavior of females may come at an energetic cost to them. This study adds to growing evidence of lizards' vulnerability to global warming, particularly during reproduction when females are already paying a substantial cost.

High-mountain altitudinal gradient influences thermal ecology of the Mesquite Lizard (Sceloporus grammicus)

The thermal requirements of ectotherms may vary among species due to adaptation to different thermal environments. Nevertheless, some of these requirements are evolutionarily conserved, leading organisms to compensate behaviorally for harsh environmental conditions. High-mountain systems provide temperature gradients that allow for studies of evolutionary and plastic variation in thermal ecology under natural conditions. We evaluated the thermoregulation strategies of Sceloporus grammicus Wiegmann, 1828 at three points (2600, 3100, and 4150 m above sea level) along an altitudinal gradient. We found that the thermal quality of the site and the body temperatures of lizards are influenced by altitude and decrease with increasing elevation. However, lizards from the three different elevations have similar thermal requirements. High-altitude lizards have lower thermal accuracy and efficiency indices compared with those from the lower sites, owing to the low thermal quality of their environment. Nevertheless, they are efficient in thermoregulation, increasing their body temperature above the ambient temperature. We found that pregnant females from all three elevations had similar preferred body temperatures. Compared with nonpregnant females and males, they exhibited lower preferred temperatures and more accurate thermoregulation. The wide altitudinal distribution of S. grammicus is thus not caused by variable thermal requirements. Instead, the wide repertoire of physiological and behavioral strategies of these lizards allows this species to successfully inhabit contrasting environments.

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.

To warm on the rocks, to cool in the wind: Thermal relations of a small-sized lizard from a mountain environment

Rising temperatures accompanying global climate change are expected to affect mountain lizards. Therefore, basic information on how these ectotherms deal with their thermal environment is important for further management. We conducted a field study to evaluate how body temperature of the small-sized mountain lizard Eurolophosaurus nanuzae relates to the thermal environment. After capture, the body temperature of the lizards was measured immediately, quickly followed by the substrate and air temperatures, wind intensity, and solar radiation at the capture locations. Linear relationships showed that the body temperature of individuals was positively related to rocky substrate temperatures but negatively related to wind speed. However, air temperature and solar radiation were unrelated to body temperature. Although the substrate is an important heat source for E. nanuzae, in an open environment it can reach temperatures up to 10 °C above the maximum body temperatures of lizards, and can thus be a low-quality thermal substrate. However, individuals seemed to use wind as a cooling source to counterbalance the risks of overheating from high substrate temperatures. As the montane environment that E. nanuzae inhabits seems to have hotter temperatures than those preferred by the species, lizards should benefit from the cooling winds to keep their body temperature at appropriate levels. Different to previous studies that evaluated wind effects on body temperatures of lizards, our results showed that winds seemed to promote thermoregulation for E. nanuzae.