David Ledesma is one of our 2021 Stengl-Wyer Fellows. With his advisor Dr. Melissa Kemp, he studies the responses of herpetofauna (non-avian reptiles and amphibians) to environmental changes, and the long-term responses of herpetofauna over the last 21,000 years. As part of the Stengl Wyer Endowment, the Stengl Wyer Fellows Program supports year-long fellowships for doctoral candidates pursuing dissertation research in the area of Diversity of life and organisms in their natural environments.
1. Tell us where you came from before UT, and what you studied then?
I was actually at UT previously before starting my PhD in the Evolution, Ecology, and Behavior program. I graduated from the Jackson School of Geosciences with a B.S. with special honors in general geology. I completed an honors thesis under the supervision of Dr. Chris Bell investigating variation in the skulls of alligator lizards and the phylogenetic relationships of a fossil alligator lizard from southern California.
2. What got you interested in studying the responses of herpetofauna to environmental changes?
I’ve been interested in herps (lizards, snakes, frogs, salamanders, etc.) since I was young. I think they’re beautiful and fascinating creatures. They’re also very important for maintaining healthy ecosystems and provide services to humans such as pest control, seed dispersal, and the study of many species can help us gain significant medical insights that benefit humans. Unfortunately, the environment that herpetofauna live in is changing rapidly and many species are finding it hard to adjust to these changing conditions. We’ve already observed an increase in the rate of extinction and extirpation (local extinction) of many herpetofauna species in recent times. Extirpation and extinction of these herpetofauna species represents a great loss to the ecosystems that they once inhabited, but also represents a great loss to us humans who benefit from them. Through my research, I seek to understand how herpetofauna responded to environmental changes in the past to gain insights on how they will respond to current environmental changes and how we might mitigate the increasing number of extirpations and extinctions of herpetofauna species today.
3. Does Texas present a unique situation, challenge or benefit for your research?
I use information from fossils to understand how herpetofauna responded to past environmental changes over the last 20,000 years. Fossils can be used to extend our temporal study interval and serve as a means by which to investigate how past biota responded to environmental changes over long-time scales. Texas has a rich fossil record from the Pleistocene (last 1.8 million years) which is incredibly valuable for gaining insights from the past. One reason Texas has a rich Pleistocene fossil record are the many cave systems in Texas that protect the fossils inside them from weathering and erosion. My study site is Hall’s cave in Kerr County Texas. This is an exceptional cave that preserves a nearly continuous record of the last 20,000 years and has provided important insights on how Texas and its biota have changed over that time interval. Texas landowners, like the Hall family, who have invited researchers to work on their land have helped us make significant discoveries and have helped me to work towards my research goals.
4. How do the Biodiversity Collections at UT figure into your work?
Because I use fossils in my research, an important first step for me is identifying what type of organism those fossils represent. The comparative skeletal collections at UT curated in the Biodiversity Collections and the Vertebrate Paleontology Collections have been invaluable for my research goals. The comparative skeletal material in these collections have allowed me to better understand variation in the skeletal system of modern herpetofauna in order to identify fossil herpetofauna remains. The comparative skeletal material also allows me to gain insights on the relationship between growth of different bones and body size. This has allowed me to create models to estimate body size of fossil herpetofauna and test whether there were significant changes in body size through time. These comparative skeletal collections are derived from live organisms collected at various field sites, so field labs like Brackenridge Field Lab and Stengl Lost Pines play a critical role in my research.
5. Where do you see your research agenda heading here at UT?
I utilize a multipronged approach (morphology, fossil abundance, and paleogenomics) to detecting changes in past lizard and salamander diversity. Thus far, I have I have shed new light on the diversity of lizards from Hall’s Cave using morphological data and found that the lizard community has changed through time. In addition to my morphological fossil identifications, I am currently using ancient DNA to identify fossil lizard and salamander taxa from Hall’s Cave, thereby integrating morphological and genetic data. This allows me to test the relative abilities of morphology and ancient DNA in identifying fossil herpetofauna with the potential to reveal diversity in past herpetofauna that is not accessible when using morphology alone. Additionally, I plan to employ ancient DNA data in coalescent-based modeling to reconstruct population size trajectories and investigate demographic changes in herpetofauna over long time scales.
