Variación altitudinal en las estrategias vitales de la lagartija colilarga, psammodromus algirus, en sierra nevadarelaciones entre termorregulación, velocidad de carrera y sistema inmune

Résumé

¿ Abstract This thesis studies the effect of elevation on thermoregulation, sprint speed, immune system, and their relationships, in the large Psammodromus, Psammodromus algirus, in six populations uniformly distributed from 300 to 2500 meters above the sea level in Sierra Nevada (SE Spain). We found that lizard phenology was similar along the gradient, by using standardized transects throughout the whole activity period. However, contrasting with mid and low elevation populations, activity in high populations peaked at the beginning of the activity period, probably due to limitations in the window of time for reproduction. Studies on field and thermal-gradient selected body temperatures showed that this lizard was thermally conservative in this system. Despite differences in environmental temperature, lizards could thermoregulate effectively selecting different microhabitats at different times of the day. Nonetheless, selected body temperature was always higher than field body temperature, which suggests that other factors could be constraining lizard thermoregulation ability. In fact, field body temperature was limited by environmental temperature in the highest populations. Postpartum females selected higher temperatures, which probably allows them to improve their body condition after the reproductive investment. A study on variation in body size and thermal exchange rates showed that high-elevation lizards were larger, according to Bergmman¿s clines, which predict larger body size in cold habitats, diminishing heat loss by a decrease in the body surface/volume ratio. Moreover, highland lizards, the largest, showed higher thermal inertia. On the other hand, an immune challenge only diminished selected body temperature in lizards from mid and low populations, which probably allows them to save energy, but did not affect high-elevation lizards, possibly because the cost of no-thermoregulation in a thermally-limiting habitat outweigh those of thermoregulation. Also, sprint speed was positively correlated with limb length, and negatively with body mass, so fat accumulation seems to be traded-off with the ability of fleeing from predators. However, gravid females were not slower than non-gravid females. Nevertheless, males, more conspicuous to predators, were faster than females. Elevation had no effect on sprint speed. As for the effect of an immune challenge on sprint speed, only males were affected, diminishing their speed, probably because they invest more energy than females in sprint speed. Finally, sprint speed was faster at optimal than at suboptimal body temperatures for lizards from all elevations, suggesting that thermal preferences and thermal dependence of sprint performance are coadapted. On the other hand, gravid females, which were not slower than non-gravid females at optimal body temperatures, were indeed at suboptimal body temperatures. These results confirm that sprint speed is highly conservative in elevation.