For most biology students, the conventional pathway toward initiating research entails pursuing questions in a research field in which they’re interested. Jordan Garcia, Ecology and Evolutionary Biology, however, arrived at the subject of his PhD dissertation in a decidedly antithetical manner—by pursuing the field he found most pertinent to the questions about which he was curious.
A summer spent studying gecko morphology at Michigan State University, while he was completing his undergraduate degree at Beloit College, introduced Garcia to herpetology, the study of amphibians and reptiles. Garcia soon perceived that ectotherms (animals that rely on environmental heat sources), which is the focus of substantial herpetological research, have a clear causal relationship with their local environments, making it easier for researchers to draw evidence-based conclusions.
“Before the summer I spent at Michigan State, herpetology and the study of ectotherms had not been on my radar as a potential academic field, but I soon realized that the questions I’m interested in lend themselves well to the field.”
Evolving with an Environment
The questions Garcia is exploring relate to evolution—the what and how. What causes adaptation, and how does an organism evolve to suit the changing environment? Having joined Kelly Zamudio’s lab, Ecology and Evolutionary Biology, in his first semester at Cornell, fall 2018, Garcia credits Zamudio with helping him to identify the specific theme of his research dissertation.
“During my first few weeks at the lab, I read up on the fundamental concepts of herpetology, in an attempt to familiarize myself with the subject and engage with the questions that might arise regarding these concepts.
“During my first few weeks at the lab, I read up on the fundamental concepts of herpetology, in an attempt to familiarize myself with the subject and engage with the questions that might arise regarding these concepts. Over the following days, Professor Zamudio and I mapped out my academic interests and the questions I had in mind and located the kind of research I would be most interested in.”
Consequently, Garcia began analyzing salamander emergence, a subject he felt could reveal salient information on the evolution mechanism, and perhaps even its limits. Spotted salamanders, Garcia explains, exhibit an intriguing breeding pattern. Dependent on levels of precipitation and atmospheric moisture, the amphibians rush to breeding ponds immediately after concluding their hibernation periods.
Salamanders and Local Adaptation—New York and Georgia
A substantial variance, however, exists in the breeding schedule, for example, between spotted salamander populations in Georgia and those in New York State, owing to vast differences in weather conditions. Whereas spotted salamanders conclude their hibernation periods as early as January in Georgia, salamanders do not emerge from hibernation until the middle of March in Upstate New York due to the frigid winters.
“New York and Georgia represent two geographically contrasting reaches of spotted salamander populations on the East Coast, and thus have high levels of weather-related contrasts. My aim was to evaluate possible evidence of local adaptation.”
Upon collecting nearly 300 spotted salamander eggs, each from breeding ponds in New York and Georgia, Garcia then raised the eggs at three different temperatures—10, 17, and 25 degrees Celsius—from the eggs’ hatching to the salamanders’ metamorphosis. At 10 degrees, Garcia observed, the samples failed to grow and develop. He, then, focused on the two other temperature samples. Garcia began analyzing the critical maximum (CT Max) and minimum (CT Min) for each of the specimens from both states to determine differences in tolerance levels among the salamanders.
The process involved lowering or raising the temperature for each sample, until it could not withstand a further drop or increase. Although the method ostensibly seems straightforward, Garcia contends that he had to be cautious while varying the temperatures, lest he made it far too warm or cold for the salamanders to survive. Following the salamanders’ metamorphosis, Garcia collected the water in the sample containers, which he plans to analyze in order to evaluate differences in cortisol secretion, indicating the intensity of a salamanders’ stress response to the variation in temperature.
Garcia definitively concluded that the New York samples could withstand lower temperatures than the Georgia population. This finding conveyed evidence of the dynamic process of local adaptation. On the other hand, Garcia did not find evidence of local adaptation in southern populations for greater heat tolerance. This lack of local adaptation for heat tolerance in salamanders, he explains, is similar to observations in other ectotherms.
Tolerance for Cold Temperatures versus Heat
Garcia posits that salamander populations along the eastern seaboard behave as a meta-population, with frequent migration within population subdivisions, or demes. He contends that the selective pressure of cold tolerance must be extremely high, since he found local adaptation in his study despite substantial gene flow.
Garcia also found that while the samples’ temperature variations had an impact on their CT Min, there was no evidence that the salamanders raised at 25 degrees Celsius could withstand warmer temperatures than those raised at 17 degrees. At the lower end, he posits that selective pressure to be first to the breeding pond after hibernation could explain a greater plasticity in colder temperatures. For example, if a salamander can withstand increasingly cold weather, it can arrive quicker to a breeding pond, ahead of others. Another possible explanation is that mechanisms for adapting heat tolerance are costly and do not arise as readily as those for cold tolerance. The ability to thermo-regulate may be easier in response to increased temperatures. Burrowing and evading radiation is likely easier than finding warmth during cold periods, especially at higher latitudes.
Heat Tolerance and Climate Change
A lack of similar plasticity toward warmer temperatures indicates a troubling reality. As climate change continues to result in higher average temperatures, there may be a point at which even the average temperature, especially during the summer, becomes far too warm for spotted salamanders, just as it may for a myriad of other species. Garcia defines this concept as the tradeoff hypothesis.
“Local adaptation and degrees of plasticity allow an organism to alter its structure over time to accommodate changing environments, but no organism can evolve beyond a certain point, especially not at the current pace of global warming,” says Garcia. His primary concern is that this fatal temperature level is fast approaching. Even the 25 degree samples from Georgia could not withstand an average temperature beyond 38 degrees. As temperatures increase, southern spotted salamander populations across the country are most at risk, owing to their lack of plastic response toward warmer temperatures—in conjunction with rising average temperatures in the region.
The Effect of Temperature on the Fight or Flight Hormone
Having completed the first stage of his dissertation, Garcia now plans to move forward with analyzing the salamanders’ respective stress responses. Cortisol, the fight-or-flight hormone, is responsible for adrenaline secretion within the body. Its secretion levels depend on the intensity of the scenario as perceived by the brain. Garcia’s hypothesis is that due to greater variation in weather patterns in New York, the Upstate samples will exhibit lower cortisol secretion than the Georgia samples. Garcia’s hypothesis is that due to greater variation in weather patterns in New York, the Upstate samples will exhibit lower cortisol secretion than the Georgia samples. A lack of plasticity at the warmer end, however, may prove dangerous for the New York samples, due to global temperature increases. They may be better suited to erratic weather patterns, another frequent consequence of climate change.
As the unorthodox nature of his initial approach to research suggests, Garcia is more invested in the scientific process of enquiry than he is in reaching a particular conclusion. “I try to look beyond the strictly academic purposes of my work. I find the research itself more compelling than the end result.”
Garcia is also a teaching assistant (TA) for Cornell biology. Having completed his undergraduate degree at a private liberal arts school with small class sizes, he’s interested in observing the different nature of active learning, which takes place in classes of 200 students. “For me, the most rewarding part of being a TA is engaging with students, either individually or in my discussion sections, and seeing their knowledge grow and their understanding deepen as a result of our interactions.”