Thermal ecology and evaporative water loss of the range-restricted lizard Sceloporus macdougalli (Sq

Muñoz-Nolasco, Francisco Javier

Arenas-Moreno, Diego Miguel Santos-Bibiano, Rufino Gandarilla-Aizpuro, Fabiola Judith

Posgrado en Ciencias Biológicas

Universidad Nacional Autónoma de México

Ciudad de México, MX

fjmn36@gmail.com

Bautista-del Moral, Adán

Facultad de Ciencias Químico-Biológicas

Universidad Autónoma de Guerrero

Guerrero, Mexico

Méndez-de la Cruz, Fausto R.

Laboratorio de Herpetología

Departamento de Zoología, Instituto de Biología

Universidad Nacional Autónoma de México

Ciudad de México, Mexico

Tropical lowland ectotherms tend to be physiologically more specialized than their highland or temperate counterparts, making them particularly vulnerable to changing environmental conditions. Macdougall’s Spiny Lizard (Sceloporus macdougalli) is a viviparous member of the poinsettii group with contrasting sexual dichromatism. It occurs in the Pacific lowlands of southern Oaxaca, Mexico, where it is restricted to large granite boulders in tropical deciduous forest. Despite its endemicity and evolutionary significance, information on the biology of this species is scarce. On November 2015 (end of the rainy season) and March 2018 (dry season), we conducted samplings at the locality of Santa Cruz Bamba, Oaxaca (50 m asl), to gather data on the physiological ecology of S. macdougalli. We measured field body temperatures (Tb), selected temperatures (Tset), accuracy of thermoregulation (db), thermal quality of the environment (de), thermoregulatory efficiency, thermal tolerances (CTmin and CTmax), thermal safety margins (TSM), and evaporative water loss rates (EWL) at two temperature treatments (25 °C and 35 °C). There were no differences in Tb, Tset or thermal tolerances between samplings. Also, Tset was lower than for other members of the genus (28.57 °C ± 0.216). Thermoregulatory efficiency of S. macdougalli showed a suboptimal exploitation of the thermal environment in November and extraordinarily high values in March, although this could be due to the organisms retreating into caves formed by the boulders to avoid the high temperatures from the outside. Similarly, TSM, which was already narrow in November (2.3 °C), indicated “thermal danger” in March (-3.42 °C). Even though no statistical differences were shown, mean EWL was higher at the second treatment (1.786 vs. 2.459 mg H2O/h). Our results highlight the importance of those boulders as thermal refugia for S. macdougalli and suggest that the species is prone to the effects of habitat degradation and climate change.