Seasonal and Geographic Eurythermy in a Coastal Peruvian Lizard

We contrasted the summer and winter field body temperatures of the tropidurid lizard Microlophus peruvianus at the Paracas Peninsula in southern Peru. We also compared our winter data to those gathered by >Huey (1974) at the Illescas Peninsula in northern Peru to test the hypothesis that southern lizards would tolerate lower temperatures than northern lizards. Cloud cover is more persistent in Paracas than it is in Illescas. During the austral winter, lizards at Paracas reduced surface activity to midday hours and had body temperatures below the mean set-point temperature (as measured in a photo-thermal gradient). Lizards from southern Peru were active over a wider range of temperatures than were lizards from Illescas. Mean body temperature of field-active lizards in the cloudy Paracas site was 33.0 ± 0.44 C, significantly lower than the mean field body temperature at the sunnier Illescas site (36.3 ± 0.26 C, t = −6.19, P < 0.001). Although thermal preferences tend to be conserved among related lizard species, we found considerable variation in body temperatures and activity patterns of two populations of this species.

Figure 1.

(A) Daily activity of Microlophus peruvianus during the summer, based on 5 minutes census conducted on nine 40-m-long beach transects from 0800–1400 h in Paracas (n = 4 for each time of the day).Afternoon data were not recorded because of strong southwesterly winds. (B) Daily activity of Microlophus peruvianus during the winter, based on a repeated census at 0800, 0930, 1230, 1530, and 1730 h conducted along 3 km of beach in Paracas (n = 10 for each time of the day). Each point represents one daily census; horizontal bars indicate the mean number of lizards across all days for each sampling time

Figure 2.

Number of active lizards (histogram bars), average air (thick line) and soil (dotted line) temperatures, cloud cover index (boxes above graphs) at five census times during two winter days in Paracas.A black box indicates overcast conditions (cloud cover index 1 to 3), a hatched box indicates partly cloudy conditions (index 4 to 7), and a white box indicates sunny conditions (index 8 to 11)

Figure 3.

Distribution of body temperatures for field active Microlophus peruvianus during (A) summer and (B) winter months on the sandy beach in Paracas.The mean T_bs of active lizards are indicated by the arrows in the two histograms. The cross-hatched vertical line indicates T_set measured in the laboratory

Figure 4.

Means and standard errors of (A) the d_b index indicating the average degree to which lizards experience T_bs outside the set-point range, (B) the d_e index indicating how closely the available T_es in the two locations match the set-point range, and (C) the E index of the effectiveness of thermoregulation for the two locations during the austral winter.The estimates of E differ significantly between the two locations, based on bootstrap resampling of the d_bs and d_es. Indices have been calculated for every day of observation by calculating the grand mean across hourly averages of T_es. We have assumed T_bs to remain constant throughout the study period; therefore, the d_b is a mean of calculations based on all available T_bs

Contributor Notes

(AC, MAD) Department of Biological Sciences, Florida International University, Miami, Florida 33199; and (JC) Departamento de Ciencias Biológicas y Fisiológicas, Universidad Peruana Cayetano Heredia, Av. Honorio Delgado 430, Urb. Ingenieria, San Martin de Porres, Lima, Perú. (AC) acaten01@fiu.edu. Send reprint requests to AC.

Accepted: 26 Jul 2005