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Survival of Mexican lizards at freezing temperatures


Fierro-Estrada, Natalia



Universidad Nacional Autónoma de México, Facultad de Estudios Superiores Iztacala, Unidad de Biotecnología y Prototipos, Laboratorio de Recursos Naturales, Avenida de los Barrios Núm. 1, Col. Los Reyes Ixtacala, 54090 Tlalnepantla, Estado de México, México


Posgrado en Ciencias Biológicas, Unidad de Posgrado, Edificio D, 1◦ Piso, Circuito de Posgrados, Ciudad Universitaria, Coyoacán, C.P. 04510, CDMX, México


Méndez-de la Cruz, Fausto R.

Universidad Nacional Autónoma de México, Instituto de Biología, Departamento de Zoología, Laboratorio de Herpetología, Apartado postal 70515, 04510 CDMX,

México


Tellez-Valdes, Oswaldo

Universidad Nacional Autónoma de México, Facultad de Estudios Superiores Iztacala, Unidad de Biotecnología y Prototipos, Laboratorio de Recursos Naturales, Avenida de los Barrios Núm. 1, Col. Los Reyes Ixtacala, 54090 Tlalnepantla, Estado de México, México


Freezing survival mechanisms have been widely studied in species of lizards that live above the tropical line, in middle and high latitudes, however, little is known about survival at low temperatures of lizards that live within the tropics. To cope with subzero temperatures, organisms need physiological adaptations; these strategies are closely linked to high concentrations of cryoprotective molecules, such as glucose. The objective of the study was to determine if tropical species of Mexican lizards presented freezing survival mechanisms. We raise the questions of whether the Xenosauridae family, being one of the oldest groups of lizards, presents these mechanisms and whether the Gerrhonotinae subfamily, being close to the Xenosauridae family, shares such mechanism. Therefore, we collected active lizards of the genus Xenosaurus, Barisia, Abronia and Gerrhonotus, we recorded their body temperatures throughout the year, their blood glucose levels, and determined their supercooling point. We also recorded environmental temperatures using null models calibrated in the habitats of the study species. We found that the 4 genera had high levels of glucose throughout the year. In 6 species we observed activity in the field at low temperatures, the only species in which we did not observe this pattern is the one that lives at the lowest elevation. The five anguid species were eurythermic, while the two Xenosaurus species presented stenothermic strategies. All studied species from both families showed survival to experimental freezing temperatures, regardless of their reproductive mode, which shows that tropical lizards also have adaptation to the freezing temperatures that are presented in cloud forest, high elevation mountains or low lands in tropical areas.

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