Vulnerability to climate warming of Tropidurus torquatus based on physiological and behavioral proxies

PIANTONI, CARLA; IBARGÜENGOYTÍA, NORA RUTH; NAVAS-IANINNI, CARLOS

BAHIA BRASIL

Congreso; VI CONGRESSO BRASILEIRO DE HERPETOLOGIA; 2013

Environmental changes could shift behavioral and physiological performance in ectothermic vertebrates to suboptimal levels, restricting time for activity and making these lineages particularly sensitive to global warming. Moreover, a general pattern suggests that as thermoregulatory behavior increase with latitude and altitude, tropical and low land lizards behave as thermoconformers. Thus, tropical lizards are expected to be particularly vulnerable to rapid changes and will probably suffer most of the extinctions. We examine the hypothesis that vulnerability to climate warming is inversely related to latitude using as proxies physiological and behavioral variables. We focus specifically on the effects of the rising air temperature (Ta) on the thermal biology and regulation on three populations of the species Tropidurus torquatus that, due to the species' flexible thermal physiology, are expected to present different levels of vulnerability. The variables used in this study were body temperature (Tb), the distribution of operative temperatures (Te) at each capture sites, preferred body temperature (Tp) and set-point range (Tset) estimated in the laboratory, and the effectiveness of thermoregulation (E). Field work was done along a latitudinal gradient of the Brazilian Cerrado during the reproductive season: Piracaba, SP, and Arinos, MG, where the species inhabits urban areas, and Formoso do Araguaia, TO, where it occurs in the gallery forest. The lowest Tbs were found in Piracicaba (35.3°C) although the Tb range comprises higher temperatures (32.3-41.6°C), followed by Arinos (35.8°C; 30.4-35.9 °C) and Formoso (36.2°C; 32.2-39.2°C). The Formoso population showed the lowest variation of Tb (SE=0.3°C), which can be interpreted as either accurate thermoregulation or non-regulation driven by an homogeneous habitat. The highest Tset (35.3-37°C) was found in Piracicaba, followed by Formoso (34.1-35.5°C), and Arinos (33.2-34.7°C). Most of the Tb recordings in Piracicaba fell below Tset, while at Arinos and Formoso Tb recordings exceeded Tset. Actually, and although Te ranged at all three sites similarly, the lowest values were found in Piracicaba as well as the greatest proportion of Te below Tset. Lizards in the South thermoregulate effectively (E=0.61) and achieve high Tbs. At lower latitudes where the exposure to Ta variation is low and, therefore, the ability to adapt in a changing environment is reduced, T. torquatus becomes a thermoconformer (EArinos=-0.18 and EFormoso=-0.01). Non-thermal regulation and larger proportions of Tb and Te above Tset would increase the risk of overheating with an eventual raise of Ta, precluding time of activity and possibly driving some populations to extinction.