Thermal Biology Constraints in Oviparous Lizards from Southern Patagonia, Argentina: Intraspecific Comparison of Liolaemus bibronii Populations.

MEDINA, M. AND IBARGUENGOYTIA

Manaos Brasil

Congreso; 6th World Congress of Herpetology; 2008

Geographic variation strongly influences the thermal ecology of terrestrial vertebrate ectotherms and, in particular, their body temperatures and activity levels. The quality of the thermal environment for ectotherms generally declines with elevation and latitude, and it is strongly influenced by maritime versus continental climates. In northwestern Patagonia, Argentina, the climate is dry and cold with intense westerly winds, snow in winter, and freezing temperatures most of the year with lizards found active during spring and summer. The thermal biology of one of the southernmost oviparous lizards, Liolaemus bibronii, was studied at high and low-latitude sites in Patagonia, Argentina, following the methodology of Hertz et al. (1993). For further comparisons, previously published data of field and selected body temperature of 33 oviparous and 22 viviparous populations of Liolaemids were analyzed. Liolaemus bibronii, as one of the southernmost oviparous lizards, showed the lowest field body temperature (Tb = 28.11ºC) among oviparous Liolaemids, but a higher Tb than the southernmost viviparous lizard in the world: Liolaemus magellanicus (27ºC). In addition, the Tb of L. bibronii was lower than the selected body temperature (Tsel) in both populations. The micro-environmental and operative temperatures (Te) were lower in the South showing that L. bibronii lives under thermal-environmental constraints especially at the higher-latitude site. There were differences in the average degree to which Te matches the set-point range (central 50% of the distribution) of Tsel (de, southern= 12.15; de, northern= 9.62) indicative of a higher thermoregulation effort in the southern population. The analysis of the average degree to which Tb was included in the set-point range of Tsel (db), lower than the corresponding de, indicates an active selection of the microhabitats used by L. bibronii and confirms the presence of thermoregulatory behaviours in both populations. The effectiveness of temperature regulation [E = 1 – (Mean db / Mean de)] shows that L. bibronii behaves as a moderate thermoregulator. Comparison with the rest of the genus Liolaemus did not show differences in either Tb or Tsel between oviparous and viviparous populations suggesting a conservative character in the thermal biology for the genus. However, the comparative analysis of Tb versus Tsel of Liolaemids strongly suggests that oviparous species are poorer thermoregulators than viviparous species. Accordingly the low Tb and the thermoregulation effort of oviparous L. bibronii living at latitudes up to 50°S, suggest that southern species counteract the thermal constraints imposed at high latitudes, by being viviparous.