|Counter-gradient variation in thermoregulation in a widespread chilean lizard|
Whether thermoregulation behaviour is evolutionary rigid or in the contrary evolutionary labile has been a long-standing controversy in the field of thermal biology. In squamate reptiles, including terrestrial lizard species, comparative evidence from the literature suggests that some thermal biology traits may vary adaptively across species but only a handful of studies have found significant variation in thermoregulation behaviour among populations within the same species, for example along an altitudinal gradient. In this article, we investigate geographic variation in thermoregulation behaviour between the range margins of the distribution of the widespread Liolaemus pictus lizard in Chile. The genus Liolaemus is highly diversified in South America, with more than 200 recognized species, and its thermal biology has been extensively characterized during the last decade. We compared the thermoregulation behaviour of lizards from two populations located at the warm and one population located at the cold range margin during two years, and manipulated thermal conditions in the laboratory during one year to test if the geographic variation could be due to thermal acclimation. To our surprise, we found that lizards from the cold margin preferred higher body temperatures and were as effective thermoregulators as lizards from the warm margin. We propose that this pattern is caused by "counter-gradient temperature" variation where there is strong selection for a faster life cycle in the less thermally suitable habitats from the cold margin. We compare our results with those published in the literature on Liolaemus lizards and demonstrate that more thermally challenging environments select for a higher thermoregulation effort and a more effective thermoregulation. Altogether, these data confirm that thermoregulation behaviour is evolutionary labile within and between species of Liolaemus lizards. This conclusion will be of wide interest to those interested in thermal biology of lizards and the evolution of thermoregulation behaviours.
Artacho, P., Saravia, J., Perret, S., Bartheld, J. L. and J.-F. Le Galliard. 2017. Geographic variation and acclimation effects on thermoregulation behavior in the widespread lizard Liolaemus pictus. Journal of Thermal Biology 63:78-87
Populations at the warm range margins of the species distribution may be at the greatest risks of extinction from global warming unless they can tolerate extreme environmental conditions. Yet, some studies suggest that the thermal behavior of some lizard species is evolutionarily rigid. During two successive years, we compared the thermal biology of two populations of Liolaemus pictus living at the northern (warmer) and one population living at the southern (colder) range limits, thus spanning an 800 km latitudinal distance. Populations at the two range margins belong to two deeply divergent evolutionary clades. We quantified field body temperatures (Tb), laboratory preferred body temperatures (PBT), and used operative temperature data (Te) to calculate the effectiveness of thermoregulation (E). During one year in all populations, we further exposed half of the lizards to a cold or a hot acclimation treatment to test for plasticity in the thermal behavior. The environment at the southern range limit was characterized by cooler weather and lower Te. Despite that, females had higher Tb and both males and females had higher PBT in the southernmost population (or clade) than in the northernmost populations. Acclimation to cold conditions led to higher PBT in all populations suggesting that plastic responses to thermal conditions, instead of evolutionary history, may contribute to geographic variation. Lizards regulated moderately well their body temperature (E≈0.7): they avoided warm microhabitats in the northern range but capitalized on warm microhabitats in the southern range. We review literature data to show that Liolaemus species increase their thermoregulation efficiency in thermally challenging environments. Altogether, this indicates that habitats of low thermal quality generally select against thermoconformity in these lizards.