To heat or to save time? Thermoregulation in the lizardZootoca vivipara(Squamata: Lacertidae) in different thermal environments along an altitudinal gradient

Abstract

Behavioural regulation of body temperature in thermally heterogeneous habitats requires different amounts of time that could otherwise be dedicated to foraging and social activities. In this study I examined how four populations of the lizard Zootoca vivipara along an altitudinal gradient (250-1450 m) adjust their thermal-physiology traits and thermoregulatory behaviour to compensate for increasing time costs of thermoregulation. I focused on variation in several physiological (set-point temperature, heating rate) and behavioural traits (microhabitat selection, basking frequency, extent of thermoregulation). To estimate potential time spent basking and foraging by lizards that were not employing any behavioural compensatory mechanism, I used a simple biophysical model of thermoregulation, including information about operative temperatures at the study sites, selected temperature range, and heating/cooling rates. Time costs of thermoregulation for each population were calculated as potential time spent basking relative to time spent foraging. Operative temperatures varied among study sites, resulting in different time costs of thermoregulation. Lizards at 1450 m should spend about 50% more time basking than those at 250 m. I found that the only mechanism which potentially compensated for the higher time costs incurred at high altitudes was a shift in the choice of basking sites. Lizards thermoregulated with similar accuracy and effectiveness over the 1200-m altitudinal range, indicating that there were no adjustments in the extent of thermoregulation. The observed basking frequencies of lizards were highly correlated with potential time spent basking without behavioural adjustments, suggesting a minor compensatory effect of thermoregulatory behaviour. Lizards responded to higher time costs of thermoregulation primarily by allocating different amounts of time to basking. These results suggest that Z. vivipara regulated body temperature at the expense of time that could be devoted to other activities. 492Résumé : Le contrôle comportemental de la température du corps dans les habitats où prévalent des températures hété-rogènes entraîne des dépenses variables de temps qui pourrait être utilisé à d'autres fins, comme la recherche de nourriture et les activités sociales. J'ai tenté de déterminer comment les lézards Zootoca vivipara de quatre populations réparties le long d'un gradient thermique altitudinal (250-1450 m) ajustent leurs caractéristiques physiologiques thermiques et leur comportement thermorégulateur pour compenser les coûts croissants en temps de la thermorégulation. J'ai examiné plus particulièrement la variation de plusieurs caractéristiques physiologiques (températures de consigne, taux de réchauffement) et comportementales (choix d'un microhabitat, fréquence des bains de soleil, importance de la thermorégulation). Pour estimer la durée potentielle du temps consacré aux bains de soleil et à la recherche de nourriture chez les lézards qui n'avaient pas recours à des mécanismes comportementaux compensatoi...

Geographical differences in maternal basking behaviour and offspring growth rate in a climatically widespread viviparous reptile

“…Similar responses are observed in other reptiles. For example, in the viviparous common lizards (Zootica vivipara), females from high altitude populations spend 50% more time basking than those from low altitudes (Gvozdik, 2002), while in the oviparous water dragons (Physignatus lesueurii), mothers dig nests more superficially at high altitude than at low altitude, thus compensating for the climatic differences between altitudes (Doody et al, 2006;Doody, 2009). …”

“…As a consequence, local adaptations in maternal effects should be common in widespread species (e.g. Gvozdik, 2002;Doody et al, 2006;Doody, 2009). In viviparous reptiles it remains unclear, however, whether populations that have evolved in different climatic conditions will exhibit locally adapted maternal basking behaviour or locally adapted gestational thermal effects on offspring development.…”

Thermoregulation and activity pattern of the high-mountain lizard Phymaturus palluma (Tropiduridae) in Chile

“…It is well known that lizards from cooler habitats can compensate the high cost of thermoregulation by increasing basking time and using microhabitats differentially (HERTZ & ZOOLOGIA 27 (1): 13-18, February, 2010 HUEY 1981, CHRISTIAN et al 1983, DUNHAM et al 1989, ADOLPH & PORTER 1993, 1996, BAUWENS et al 1996. Additionally, lizards can change body posture and/or body orientation to the sun (BAUWENS et al 1996, GVO•DÍK 2002, and change activity patterns ( VAN DAMME et al 1989, BAUWENS et al 1996. Phymaturus palluma showed a clear sex difference in activity patterns, but not in T b .…”

Thermal biology of Amphisbaena munoai (Squamata: Amphisbaenidae)

“…The idea that different species of lizards maintain a certain "optimal" temperature was predominant until the mid-20 th century; however, it has since then been shown that there is no single optimal temperature but rather several optima depending on the activity (Rocha et al 2009). The extent of thermoregulation is also known to vary intraspecifically due to various factors, such as altitude (Gvoždík 2002), seasonality (Huey and Pianka 1977), habitat structure (Sears and Angilletta 2015), sex , or even competition with other species (Žagar et al 2015). Moreover, an individual may be a thermal specialist at specific times but a thermal generalist overall throughout the year (Angilletta 2009).…”