Thermal biology, activity, and population parameters of Cnemidophorus vacariensis (Squamata, Teiidae), a lizard endemic to southern Brazil

Abstract

ABSTRACT. We investigated the following aspects of the biology of a population of Cnemidophorus vacariensis Feltrim & Lema, 2000 during the four seasons: thermal biology, relationship with the thermal environment, daily and seasonal activity, population structure and growth rate. Cnemidophorus vacariensis is restricted to rocky outcrops of the "campos de cima da serra" grasslands on the Araucaria Plateau, southern Brazil, and is currently listed as regionally and nationally threatened with extinction. Data were collected from October 2004 through September 2007 in the state of Rio Grande do Sul. Sampling was conducted randomly from 08:00 a.m. to 6:00 p.m. The capture-mark-recapture method was employed. The lizards were captured by hand, and their cloacal temperature, sex, snout-ventral length (SVL), mass, and the temperature of their microhabitat (substrate temperature and air temperature) were recorded. Individuals were then marked by toe-clipping and released at the site of capture. Body temperatures were obtained for 175 individuals, activity data for 96 individuals, and data on population structure and growth for 59 individuals. All data were obtained monthly, at different times of the day. Cnemidophorus vacariensis average body temperature was 23.84°C, ranging between 9.6 and 38.2°C. Temperatures ranged between 21 and 29°C. The correlation between external heat sources, substrate and air were positive and significant and there was a greater correlation between lizard's temperature and the temperature of the substrate (tigmothermic species). The relatively low body temperatures of individuals are associated with the climate of their environment (altitude up to 1,400 m), with large variations in temperature throughout the day and the year, and low temperatures in winter. The average body temperature observed for C. vacariensis was low when compared with that of phylogenetically related species, suggesting that the thermal biology of this species reflects adaptations to the temperate region where it lives. The monthly rates of activity of lizards were related to monthly variations in the ambient temperatures. Our data suggest that the daily and seasonal activity of C. vacariensis result from the interaction between two factors: changes in the environment temperature and the relationship between individuals and their thermal environment. The population structure of C. vacariensis varied throughout the study period, with maximum biomass in January and maximum density in February (recruitment period). The sex ratio diverged from the expected 1:1. The growth analysis showed a negative relationship between the growth rate of individuals and the SVL, revealing that young individuals grow faster than adults, a typical pattern for short-lived species. The population studied showed a seasonal and cyclical variation associated with the reproductive cycle. The life strategy of C. vacariensis seems to include adaptations to the seasonal variations in temperature, typical of its environment. KEYWORDS.Body temperature, grow...

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“…Our results corroborate the preference of C. vacariensis for rocky outcrops with herbaceous vegetation, given the positive effect of herbaceous coverage on occupancy of the species. This result was expected, due to the preference of C. vacariensis for rocky outcrops of open areas (Caruccio et al 2010(Caruccio et al , 2011, where almost all individuals may be found under rocks (Caruccio et al 2010;this study). Species of lizards adapted to open areas are often restricted by forested areas, such as the sand lizard (Lacerta agilis), which occupies only open areas or edges of vegetation areas due to thermoregulation difficulties (House & Spellerberg 1983).…”

“…It is known that substrates shaded by arboreal vegetation absorb less amount of thermal energy, making it impossible for species that thermoregulate to reach optimal temperatures (Singh et al 2002 ). In the same fashion, C. vacariensis depends on the rocky substrate to thermoregulate, and shading the rocks would impair thermoregulation (Caruccio et al 2011). This reinforces the reason why C. vacariensis mainly occupies rocky outcrops with herbaceous vegetation.…”

“…The species reaches up to 81.8 mm snout-vent length and it is an active forager, feeding mainly on arthropods (Schossler 2006). The species is diurnal, presenting a high degree of habitat specificity, restricted to sunny rocky outcrops in grassland areas (Caruccio et al 2011). Loose rocks constitute an important resource for different species in rocky outcrops (Gilioli et al 2018), especially for reptiles, since they are the main heat source for thermoregulation and protection against windy conditions, thus preventing desiccation.…”

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“…The differences of activity found between seasons are something common among lizards (Rose, 1981;Huey, 1982;Adolph & Porter, 1993;Silva & Araújo, 2008). In warmer seasons (spring and summer), there is an increase in activity rate, while in colder seasons (autumn and winter), there is an increase in inactivity rate and therefore reduced activity (Vieira et al, 2011;Caruccio et al, 2011). The highest activity rates in spring and summer may be related to the reproductive season and the appearance of hatchlings, since the number of active lizards is usually higher during the reproductive seasons than in non-reproductive seasons (Tanaka & Nishihira, 1987).…”

“…borelli and H. darwini, Cruz et al, 2005;H. darwini, Aguilar & Cruz, 2010) and other species from temperate regions, such as Contomastix vacariensis (Caruccio et al, 2011) and Tropidurus catalanesis (Vieira et al, 2011), use shelters not only for protection from predators but also for foraging activities and thermoregulation (Marquet et al, 1990).…”