Cordylid lizard thermoregulation
Does melanism matter?
Melanistic (or uniformly black-colored) species of cordylid lizards in the southwestern Cape of South Africa are generally distributed on cooler mountain tops and in peninsular areas, whereas lighter-colored congeners are found in warmer inland areas. The aim of my research was to study the thermal biology of these closely-related species and test the hypothesis that higher skin absorptivity of melanistic species provides a thermal advantage compared to lighter species in cooler areas. I modeled the effects of skin color difference between Cordylus niger and Cordylus cordylus using a steady-state energy balance equation and found that as expected from biophysical principles, melanistic lizards reach higher equilibrium temperatures than non-melanistic ones under various environmental conditions. The greatest differences in body temperature were predicted under highest incident radiation levels and low wind. After establishing that body temperatures of live lizards measured under controlled and natural conditions were in close agreement with the model predictions, the next question became…
Is the behavior of these lizards in the direction expected from the melanistic model predictions? In other words, does the melanistic trait constrain or facilitate thermal balance in field conditions? The combination of operative and body temperatures in the field with preferred body temperatures (in a laboratory thermal gradient) for Cordylus niger, C. oelofseni and C. cordylus indicated that all species were active thermoregulators in summer and winter. All species thermoregulated at a higher level in winter, although severe thermal constraints of the environment greatly reduced accuracy and effectiveness. Despite its small magnitude, the effect of melanism appeared advantageous in cold conditions rather than disadvantageous in warm conditions, especially for species such as C. oelofseni (montane species) in which operative temperatures frequently fell below its critical thermal minimum in winter.
To learn more about thermal melanism, go to: http://www.scitopics.com/Thermal_melanism.html
Sea turtle energetics
Nest environment
Olive ridley (Lepidochelys olivacea) turtles are known to nest in massive synchronous events (~1000 to 100 000 individuals or more!) at a few beaches in the world. Nancite, in the northwestern coast of Costa Rica, is one of these unique nesting grounds for the species. However, the hatching success of nests deposited during these aggregated events is typically low and the underlying reasons are still not clear. My research involved monitoring temperature, oxygen and carbon dioxide partial pressures of in situ nests as well as nests relocated into a hatchery with clean sand throughout incubation. Differences, although small in magnitude, were found between in situ and hatchery nests and seemed to indicate that an additional factor such as microbial activity may have affected eggs early in incubation and caused the low hatching success of beach nests.
Hatchling metabolism
Most studies of energy metabolism in sea turtles focus on juvenile and adult females, whereas little is known about the field energetics of hatchlings. My research aimed to estimate the cost of dispersal of olive ridley hatchlings. The dispersal is composed of three phases: the emergence from the nest cavity, the crawling on the beach towards the ocean and the “frenzy” state swimming phase to reach deeper waters. I used the doubly labeled water (DLW) technique to estimate these costs and found that the dispersal phases were ~ 4-7 fold the resting metabolic rate and that the cost of swimming was higher than the cost of crawling. The study emphasized the importance of estimating energetic costs of free-living sea turtles at different life history stages and gave a first estimation of how long hatchlings can rely on their yolk reserves before having to feed.