Joseph Franckum and Professor Kent Hatch, Integrative Biology
Examining the ratios of stable isotopes (non-decaying atoms with extra neutrons) in animal tissues can yield important information about an organism, such as detecting diet change or establishing migratory origin. Information gathered from these studies help develop future practices to care for certain species. A better understanding of an animal’s dietary capabilities will improve animal techniques.
Though these stable isotope studies have been useful for many different organisms, there have not been enough studies that examine the effects of temperature. Cold-blooded animals (ectotherms) do not generate their own body heat. As a result, their metabolisms vary depending on their climates, which can affect stable isotope studies. If this happens in a study involving isotope analysis, results can be flawed. To be accurate with these future studies, we conducted an experiment to determine the stable isotope turnover rates at different temperatures by using geckos as a model for ectotherms.
The protocol of our experiment consisted of placing 18 geckos in three different temperature controlled chambers (six geckos per chamber). The geckos were acclimatized for 10 days. Meanwhile, these geckos were fed a diet of crickets. These crickets were fed a known radio labeled food source that consisted mostly of corn. Then, to change the geckos’ isotope consumption, their diet was changed to mealworms. These mealworms were fed another known radio labeled food source that consisted mostly of wheat. We then measured the isotopes of carbon-13 and nitrogen-15 by collecting and analyzing samples of the geckos’ feces, breath, uric acid and tail. This change in the geckos’ diet altered what isotopes were being consumed. By examining the differences in each diet’s isotopes, we could make conclusions as to the effects of temperature on a gecko’s dietary pattern.
The results of this experiment showed some interesting results. The analysis of nitrogen is still in progress, but we were able to get data for carbon-13 ratios. There was a significant difference in isotope ratios between the cricket and the mealworm diets. This was expected. However, the results of these changes were the opposite of what we hypothesized. We predicted that the warmer temperatures would have the quickest stable isotope turnover rate on ectotherm tissue, but the opposite was true; the carbon-13 half-life increased as temperature increased. In other words, the warmer the temperature, the longer the stable isotopes stayed inside the gecko.
Because of the unexpected data from our experiment, we think that more study should be done. It is possible that the geckos in the warmest temperature had the slowest turnover rate because their food was processed the quickest. Ectotherms at a higher temperature have higher metabolisms, so undigested food, what we collected in our experiment, gets excreted more quickly. Thus, there is less time for radio labeled food to be incorporated into the body. The tail and uric acid samples were used to help determine if this scenario was the case or not, but the length of our experiment was too short. By carefully studying further, we can answer our questions.
Though conducting this experiment yielded valuable information, sometimes collecting data proved to be difficult. Collecting lizard samples was not as simple as putting things in tubes and labeling them. Often, things did not go as we had planned. For example, to collect a gecko’s breath, we needed bottled oxygen, but we had run out of oxygen in the beginning of our tissue sampling. Other times, the mass spectrometer, what we used to analyze our samples and collect data, was broken. These situations put our experiment on hold, and we could not proceed until they were fixed. I learned that it is wise to start experiments early and be prepared for unexpected problems.
Because we want this study to help future studies involving stable isotope analysis, we wish to share our results. A poster of this research will be presented at the Society for Integrative and Comparative Biology meetings in Phoenix, AZ on January 6, 2007. Additionally, this study will be submitted for publication to the journal Rapid Communications in Mass Spectrometry. Interestingly, there is another group at a university that is conducting a very similar experiment to ours. We hope to be published first, but I still find it interesting that there are other groups who understand the significance of the project as well. I am curious to see their results.
I feel very good about the research that was done. By examining the effects of temperature on ectotherms, we can improve stable isotope techniques. This information will be helpful to organisms in the wild. Moreover, this technique allows studying on animals without harming them. This can be especially useful for studies involving endangered organisms or organisms with a small population. More research may need to be done to understand more details about stable isotope ratios in cold-blooded animals, but the future is very encouraging.