These projects describe research Natasha has worked on. We are a lab of independent scholars, so you will find a wider range of projects in progress in the lab beyond those listed here if you explore the People in the lab.
How does the variation we can see within species today scale up to the differences between species that accumulate over time? That question forms the core of my active research interests. I approach the question from two perspectives. First, I document and interpret the only evidence of what happens to phenotypes on 1000+ year time scales: the fossil and zooarcheological record. Second, I document standing variation in analogous phenotypes within species of extant vertebrates and test its relationship to modern climatic, phylogeographic, and ecological variables.
Fossils of the Bighorn Basin
In the fossil record, I primarily work to understand how unbranching lineages (species or linked anagenetic species) change over time and in relation to their environment. Such studies are only possible in richly studied, exceptional fossil records such as that of the Bighorn Basin, Wyoming. There, my research is focused on changes in the dentition of lineages of small mammals through the climate change of the Paleocene-Eocene Thermal Maximum (PETM) ~56 million years ago (more on the PETM here).
In summer field seasons we collect fossils of these small mammals through intensive screenwashing efforts. Back in the lab, I digitize these fossils via microCT then use a series of morphometric analyses to quantify differences in morphology across species and over time (Vitek et al., 2017). Within lineages, some aspects of shape evolve in sync with changes in climate. I am currently expanding analyses to test if individualistic patterns of response to this climate change can be predicted by factors such as trophic category, biogeographic history, and development.
A side effect of these morphometric analyses is a rigorous identification process that accounts for intraspecific variation. This foundational taxonomic and systematic work contributes to an unparalleled collection of data regarding the changing abundance and distribution of small mammals during the high-magnitude climate change of the Paleocene-Eocene Thermal Maximum.
Extant Small Mammals
Biological interpretations of the fossil record, including population boundaries and processes like adaptation, are long-standing challenges for paleontologists. My approach to this challenge is to use spatial variation in extant species as an analogue for the temporal variation preserved in the fossil record. If similar drivers are at work over both space and time, then they should leave behind a comparable patterns of spatial and temporal variation.
I work to understand how biological processes shape intraspecific spatial variation in traits that fossilize well, particularly tooth morphology. The goal of this research is to develop models of the morphological patterns that intraspecific processes leave behind.
The first publication from this line of research looked at grasshopper mice (Onychomys leucogaster). Currently, I am modelling the relative contribution of population differentiation and potential climate-related evolution in the widespread generalist deer mouse (Peromyscus maniculatus). I am collaborating with researchers at Texas Tech University to sequence ddRAD-seq libraries for museum specimens with associated climate data and teeth. Together, these different sources of variation will be used to evaluate whether range shifts (modeled by phylogeographic data) or in-situ evolution (modelled by climate-related variation) are a more likely explanation for the intraspecific change in extinct species. New research directions are exploring the role of phenotypic plasticity in dental variation.
Through the Turkana Basin Institute, I collaborate on various studies of vertebrate fossils from the Turkana Basin, Kenya. You might find me or members of the lab working to characterize mammalian diversity in a new Oligocene site, Topernawi, and compare it to what we know about diversity in other East African sites. You might find one of us contributing morphometric analyses or screenwashing help to other projects ongoing in the basin. Together, the goal of most of these projects is to better understand how vertebrate diversity in Africa came to be.
Soft-shelled turtles (Testudines: Cryptodira: Trionychidae) have a fossil record spanning six continents and 125 million years of geologic time. Despite that wealth of opportunity, accurately discerning species limits and sifting out broader patterns of evolution from intraspecific variation and homoplasy is a major challenge. With international colleagues in Russia, Japan, and Switzerland, I take the approach of incorporating evaluations of intraspecific variation into taxonomic evaluations and phylogenetic analyses of Asian and North American fossils of soft-shelled turtles from the Cretaceous through the Miocene. Currently, I am also using their rich North American record as a venue for mentoring undergraduate research. Results include a comprehensive review of the North American fossil record of trionychids (Vitek and Joyce, 2015) and the links between patterns of gigantism, high diversity, and warm climates (Vitek, 2012). To get a sense of what gigantism means for soft-shelled turtles, imagine a turtle the size of the the one in this video living in Wyoming ~50 million years ago.
Recently lab members started looking at new ways of quantifying the distinctive shell surface patterns of soft-shelled turtles as a new way of documenting their diversity in the fossil record.
The Eastern Box Turtle (Terrapene carolina), is a long-standing example of the difficulty of categorizing intraspecific variation across space and time. The classification of extant populations is still contentious after over 250 years of study. Significant amounts of geographic, allometric, and sexually dimorphic variation all contribute to complexity within the species. A relatively abundant Pleistocene record further complicates evolutionary interpretations rather than clarifying the history of the species.
My approach to understanding spatiotemporal evolution in Terrapene carolina is to quantify variation of carapace shape, a phenotypic system that can be equally applied to fossil and modern record. Using geometric morphometrics and metadata available in museum collections across the United States, I am placing temporal variation in the context of multiple sources of variation and previous interpretations of the fossil record. I am currently working to understand how the presence of two sympatric morphotypes of Terrapene carolina in the Pleistocene relates to extant morphological diversity within the species.
As an undergraduate, I worked on a small project with Drs. Jakob Vinther, Jim Schiffbauer, Derek Briggs, and Rick Prum about the preservation and color patterns of a fossilized feather from the Messel Shale. We were able to put together a model to explain the red-and-white, striped coloration of an extremely well-preserved fossil by integrating taphonomy, microscopy, and physics. Our work went into a paper, “Exceptional three-dimensional preservation and coloration of an originally iridescent fossil feather from the Middle Eocene Messel Oil Shale”.