Record Details

Auth, David Leslie
Thermal Biology of the Turks and Caicos Islands Rock Iguana, Cyclura carinata
University of Florida
Ph.D. Dissertation
Dipsosaurus dorsalis;Amblyrhynchus cristatus;Sauromalus obesus;Ctenosaura similis;Ctenosaura hemilopha;Iguana iguana;Cyclura cornuta stejnegeri;Cyclura pinguis;Conolophus pallidus;Conolophus subcristatus;Cyclura carinata carinata;physiology
The ecological, ethological, and physiological thermal biology of Cyclura carinata, a large, tropical, herbivorous iguanine lizard, was investigated on Water Cay in the Caicos Islands and in Gainesville, Florida. The study lasted from June, 1974, until September, 1976, and included four field trips totaling twenty weeks. Far-field transmitters were placed in the coelom or gut of free-ranging adult iguanas (675-1864 g) for long-term monitoring of core body temperature (Tb ) in the field. Mean regulating phase Tb ranged from 38.0 to 39.7 C (February-October), quite high compared with most other iguanids. Stenothermia was pronounced, with a mean, regulating phase Tb range of only 3.3 C. Maximum voluntary Tb, 43.8 C, was only 2.4 C below the CTMax. The CTMin, 12.8 C, almost equaled the lowest recorded environmental temperature. Iguanas were initially hyperthermic in both the field and a thermal gradient, the former the possible result of bacterial infection or a transmitter meal and the latter of thermoregulatory learning. Individual differences in regulating phase Tb were partially due to variable vegetational cover and, perhaps, egg development in females. Mean operant Tb's did not correlate perfectly with seasonal change in the ambient thermal environment. Mean regulating phase field Tb exceeded mean preferred Tb. The latter did not change with Gainesville seasonal acclimatization, whereas winter variance of mean Tb was less than summer variance in both field and thermal gradient. Mean regulating phase Tb was inversely correlated with cloud cover time, the correlation improving with seasonal cooling. Tb was nearly independent of shaded air temperature. Heat transfer through the dorsal and ventral body was examined using three transmitter placements on penned iguanas. Heat was usually gained dorsally and lost ventrally; iguanas were thigmothermic only 20.7 percent of their active period, usually in combination with heliothermia. Individual frequency distributions of regulating phase maximum and minimum Tb's were commonly skewed positively and negatively, respectively, whereas inclusive individual distributions were usually negatively skewed. Standard deviations were slightly but not significantly greater for mean minimum than mean maximum Tb's. Change in Tb between any two consecutive maxima was positively correlated with change in two consecutive minima, with the first minimum immediately before or after the first maximum. Individual mean maximum and minimum Tb's were directly and linearly correlated, the regression line extrapolating to approximately the maximum voluntary tolerance. These results are discussed in terms of dual-limit thermoregulation. Iguanas were diurnally active all year and rarely escaped into burrows due to overheating. Mean regulating phase heating was 1.15 times faster than cooling and 3.0 times slower than heating during morning basking. Iguanas also heated faster than they cooled in a constant temperature chamber, both when restrained and when permitted to move about. Maximum Tb commonly occurred during late afternoon basking. This and other results indicate that surface rather than core body temperature is regulated. Both length and rate of travel were independent of mean Tb between 35.0 and 40.5 C. Arboreal climbing, burrow excavation, defecation, drinking, feeding, nasal salt gland secretion, and panting were also examined in relation to mean Tb. Thermoregulatory behaviors and postures were described. A photothigmotron was constructed to quantify iguana light shadow and substrate contact in a controlled thermal environment. Shuttling and sun orientation were examined. A time-motion study revealed the low activity rate of penned iguanas and activity partitioning between foraging, social, and thermoregulatory behaviors. Thermoregulatory behavior was quite similar to other heliothermic iguanids. Resting and maximum oxygen consumption, and heart rate and oxygen consumption during recovery from maximum exercise were determined at different Tb's. Iguanas fatigued rapidly during maximum exercise, yet rarely developed large oxygen debts in the field. Heart rate increment, initial rate of recovery, and oxygen scope were greater in the preferred Tb range.