×Reptiles have been considered “cold-blooded” for centuries, and even Linnaeus in his Systema Naturae placed them together with amphibians. However, from the ’40 of the previous century, a few researchers started to measure reptiles body temperature in the field. They soon discovered that reptiles can maintain their body temperature warmer than air temperature and to keep it constant over a considerable amount of time mainly by behavioural thermoregulation. In the following decades, thousands of articles investigated reptile thermal ecology. In recent years, along with the worldwide raising interest in the potential adverse effect of climate change on biodiversity, studies on reptile thermal ecology are gaining increasing scientific value, for example by showing that up to one-fifth of all reptile populations may go extinct by the end of the century. By contrast, water balance in reptiles has received comparatively less attention. Indeed, water has been often considered an amphibian’s issue, and temperature a reptile’s one. However, in recent years, several works are exploring the potential adverse effects of water shortage, dehydration, and rainfall regimes on reptile biodiversity, distribution and activity. Furthermore, climate change is predicted to increase the frequency of droughts and heatwaves, especially in some areas like the Mediterranean basin. Thus, the time has come for research on reptile thermal ecology to intertwine as much as possible with other aspects of their ecology, physiology and life-history. Indeed, only a more comprehensive research framework may allow us to gain deeper insight on reptile biology, and to develop more powerful predictive and managing tools to understand if and how this group of animals will react to the future climatic and environmental challenges they face. In the present work, I describe and discuss the results of six investigations aimed at reinforcing our understanding of reptile thermal ecology, water balance, and the potential interactions between these two fundamental aspects of reptilian biology. The body temperature of reptiles can be collected in many ways. One of the most common methods is to use a thermocouple to measure the cloacal temperature. Nowadays new tools, like portable infrared cameras, are significantly improving several sectors, from industry and defence to diagnostic medicine. Research on reptiles may benefit from incorporating infrared data, that allows for new and alternative ways to study thermal ecology. A first big challenge is to prove that new tools are reliable and comparable with the most common and widespread ones. Here, the first step has been to demonstrate the robust relationship between cloacal and infrared readings. The investigation then moved in the field to investigate, using infrared imaging, a poorly studied aspect of antipredator behavior of lizards. Indeed, when lizards hide from a predator, it is likely that their body temperature decreases with time. Such a decrease in body temperature may represent a cost in terms of fitness if lizards are forced to waste time thermoregulating after each predation attempt, losing the opportunity to feed or mate. In this work, it has been quantified for the first time the decrease in body temperature that lizards suffer while hiding from the predator. Another line of investigation in this project focused on the thermal ecology, water balance and performance of closely related species that coexist. Research on several groups of organisms indicates that coexisting closely related species reduce potential competition by segregating in time or space or by changing enough (character displacement) to reduce niche overlap. In thermal ecology studies, depending on the case, closely related species both show conservativeness or variability in thermal preferences. Here little differences in thermal preferences were found comparing two sister species, P. bocagei and P. guadarramae collected in the same area. Similarly, they do not differ in running performance. However, these species showed more variability in their resistance to water balance. Finally, the last two studies focused on the potential interaction between thermal ecology and water balance, as well as on their inherent variability among populations. In the first experience, dehydration impaired thermoregulation in four lizard species. Indeed, dehydrated lizards reduced their body temperature and retreated more often inside the refuges. In the second study, on the lizard Psammodromus algirus, the field survey found little variation in body temperature across populations. However, lizard body temperatures showed daily and seasonal flexibility. On the contrary, resistance to water loss increased with altitude but showed no seasonal variability. In summary, the investigations presented in this thesis allowed to (1) validated the use of Infrared cameras in thermal ecology studies on lizards, by demonstrating the robust relationship between surface and core temperature; (2) investigated lizard hiding behavior in the field and quantified for the first time the decrease in body temperature that follows after a predation attempt; (3) quantified the difference in preferred body temperature and resistance to water loss in closely related species living in sympatry; (4) compare the running performance of such closely related species and assess their thermal sensitivity; (5) understand how and to what extent dehydration impairs thermoregulation and space use in small lizards and (6) evaluate if thermal preferences and resistance to dehydration may show variation among populations across an altitudinal gradient. The contribution of the presented works may have, potentially, methodological and ecological implications. New technologies and tools, like infrared imaging, will allow answering physiological and behavioural questions that cannot be tackled with more traditional methods. The lizard hiding behavior provides an example, investigated here. Similarly, the fact that closely related species may coexist despite little physiological and whole-organisms differentiation calls for more studies on this subject. Finally, several studies, including the last two presented here, are pointing out the potential adverse interaction between thermoregulation and water balance in several lizard species. In the following years, it will be necessary to investigate further such an interplay, especially in the light of the climatic and environmental pressures that humankind is posing worldwide on lizards.
