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This experiment is still ongoing, and the data behind it is currently being collected by Laura Kouyoumdjian and Fabien Aubret of the Station d’Ecologie Théorique et Expérimentale du CNRS, as well as Eric J. Gangloff of Ohio Wesleyan University.
Thermal physiology, hyperoxia, Iberolacerta bonnali, plasticity, thermoregulation, climate change
As climate change worsens and temperatures rise, the ability to respond to novel environments is becoming essential for all life on Earth. Ectotherms, or “cold-blooded” animals, are particularly vulnerable to environmental changes, as they rely on environmental temperatures to maintain their body temperature. Ectotherms that reside at higher elevations are facing warmer temperatures while also dealing with high-elevation hypoxia (oxygen deprivation). To study the effect oxygen availability has on ectothermic thermal physiology, we collected Pyrenean rock lizards (Iberolacerta bonnali) from high-elevation habitats. These lizards were then split into two treatments: one group was maintained at the same high elevation environment and one group was transplanted to lower elevation. We then conducted thermal preference trials on both groups in thermal arenas with a gradient of 20-60℃. We predicted that lizards transplanted from high to low elevations would prefer a warmer environment, as the increased oxygen availability would aid in maintaining a higher metabolism. While inside these arenas, thermal imaging cameras (FLIR C3 models) were used to take thermographs of each lizard every five minutes. From these thermographs, I extracted both body and head temperature data, and then analyzed it to test the effects of oxygen availability on the thermal preferences for each lizard. This data was also analyzed to test for the presence of regional heterothermy (a physiological strategy wherein ectotherms keep different regions of their bodies at different temperatures) in I. bonnali. These results are important because they can give insight into unknown mechanisms of the I. bonnali’s thermal physiology and help in understanding the mechanisms of how they adapt and respond to the novel environments created by climate change.
As climate change worsens, temperatures around the world continue to fluctuate, creating novel environments. The ability to respond and adapt appropriately to these new environments is quickly becoming an essential part of every organism's life. One group of organisms that are especially vulnerable to these new climatic conditions are ectotherms, or “cold-blooded” organisms, as they rely heavily on their surrounding environment to maintain their body temperature. Ectotherms that reside at higher elevation habitats have an even harder time adjusting to rising temperatures, as they have unique struggles that have been exacerbated by climate change, such as extreme temperatures, intense radiation, and hypoxia (oxygen deprivation) One type of defense lacertid lizards like I. bonnali have in defense to these dangers is regional heterothermy, a physiological strategy to maintain different regions of their bodies at different temperatures. This regulates the highly temperature sensitive nervous system of ectotherms. To study the effects of oxygen availability on ectothermic thermal physiology and performance, we collected groups of Pyrenean rock lizards (Iberolacerta bonnali), a threatened species endemic to high elevations, and tested how their thermoregulatory behavior and sprint performance responded to different environments.
We predict that lizards transplanted to low elevation would exhibit higher thermal preferences and voluntary thermal maxima, as the increased oxygen availability would aid in maintaining a higher metabolism. Additionally, we predict that maximum sprint speed and the optimal temperature for sprint speed would increase in the transplanted lizards, corresponding with a shift in the shape of the thermal performance curve. In terms of regional heterothermy, we predict that the head temperature will will remain more consistent relative to the body, due to brain tissues’s sensitivity to temperature changes.
This experiment began by collecting 40 male I. bonnali individuals from their high elevation habitats. These lizards were captured via the lasso method, marked with a cautery pen, and were then weighed and measured. These lizards were then split into two treatment groups: the control group of twenty individuals were maintained at high elevation and the other 20 were transplanted to low elevation where there is 25% increase in oxygen availability relative to their native habitats.
Conducted in an arena with a thermal gradient of 20-60℃ (created via four 150 Watt ceramic lamps), the preference test was used to collect data on the thermal preferences (Tpref) of the lizards in the two treatment groups with different levels of oxygen availability. Each lizard was placed in a 90 x 15 cm lane and acclimated over the course of an hour. Over the next three hours, thermal images were taken of each lizard as they moved along the lane every five minutes via a FLIR C3 thermal camera. By analyzing these images, we were also able to measure the voluntary thermal maximum (VTmax) by determining the maximum temperatures the lizards voluntarily selected. I then used thermal analysis software to extract both head and body temperature for each lizard.
For the performance tests, lizards were raced under a series of temperatures (15℃, 22℃, 29℃, 32℃, 35℃) to understand the combined impact of oxygen availability and temperature on racing performance. Lizards were ran 2-6 lengths on a race track (120 x 24 cm) while being recorded by a 25 fps camera (Sony Model HDR-XR160E). Once the running was complete, data was collected via Tracker software, and the maximum speed was calculated over a time step of 0.2 seconds.
The results of this study will give insight into the mechanisms underlying the thermal physiology of the high elevation specialist lizard Iberolacerta bonnali. This new understanding can then be used to predict future plasticity in the physiological and thermoregulatory responses in other similar species when exposed to the novel environments being created by climate change.
Data from this experiment will continue to be collected until 2021, wherein it will be presented at the Society for Integrative & Comparative Biology by Sierra Spears.
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