Mechanistic underpinnings of lacustrine brGDGT production, and proteomic vertebrate taxonomic identification of phrynosomatid lizards and arvicoline rodents

Paleoecology is a broad topic that seeks to characterize biological-environmental interactions of the past. Our understanding of modern ecology is enhanced and informed by paleoecology. Paleoecological analyses on issues such as species distribution, extinction and generation, and the impacts of climatic shifts on biotic systems serve to inform our understanding of these same issues today and into the future. Accuracy in paleoecological studies is therefore crucial to correctly characterizing biotic communities of the past so that we can better understand how those communities are the same or different today, and how geologic or climatic shifts may have influenced community stability or change. Understanding how environmental variables have influenced biotic change in the past gives researchers tools to determine conservation strategies and mediate impacts on biotic communities in the face of irreversible and significant anthropogenic climate change. Erroneous paleoecological conclusions, therefore, risk the generation of erroneous conclusions about the development of today’s biotic communities, and erroneous conservation strategies for the future of those communities. I used biomolecular and geochemical methods of analysis to interrogate three topics of research that inform paleoecological analyses: 1) Improved understanding of the environmental conditions that affect the formation of an established paleotemperature proxy—branched glycerol dialkyl glycerol tetraethers (brGDGTs)— derived from bacteria; 2) The viability of taxonomic identification of North American lizards using proteomic analysis of the collagen (I) (COL1) protein in bone, and this method’s ability to test the accuracy of morphological identifications that are the basis of hypothesized lizard biogeographic and taxonomic Quaternary stability; and 3) Application of the same proteomic method of identification to North American arvicoline rodents (voles, lemmings and muskrats) to assess the rate of amino acid substitution of COL1 in a rapidly diversified clade. Each of these topics of research resulted in a meaningful alteration of scientific understanding of the mechanisms underpinning paleoecological studies related to the respective topic. My brGDGT experiments identified the role of two different bacterial thermal classes on brGDGT production, conclusively demonstrating that brGDGTs are produced by multiple bacterial communities. The identification of these bacterial thermal classes and their biological constraints opens the door to improved paleotemperature reconstruction through the adaptation of current calibration methods to account for bacterial thermal class. Future research into brGDGT production by means of incubation experiments can be improved as a result of my identification of cold-shock as the cause of the observed failure for incubated bacteria to adapt to colder incubation temperatures. In addition to my paleotemperature work, I used proteomic analyses to de novo sequence the collagen (I) (COL1) protein for a set of North American lizards and arvicoline rodents (voles, lemmings and muskrats) to be used for proteomic species identification of morphologically unidentifiable bone material. This method of identification, colloquially known as ZooMS, uses a reference database of COL1 protein markers to distinguish between vertebrate taxa. Prior to my analysis, there was only one lizard in the reference database, and the value of using ZooMS to identify lizards in general was unknown. I demonstrated the ability to proteomically distinguish between tested species which are morphologically difficult or impossible to separate. I further found that 37% of morphological identifications of fossils purported to belong to our tested taxonomic group were erroneous. My results call into question purported species paleodistributions and hypothesized geographic and taxonomic stability of North American lizards established based on morphological identifications. My work on arvicoline rodents similarly found proteomic analysis can fully resolve species within our set of tested taxa, including between species hypothesized to have diverged less than one million years ago. I was also able to proteomically demonstrate that the extinct species, Microtus paroperarius is distinct from the extant species Alexandromys oeconomus, despite scientific opinion advancing towards synonymizing these species due to extreme morphological similarity. Together, this research program constitutes significant improvements to the accuracy of paleoecological conclusions related to brGDGT paleotemperature research, North American Quaternary distribution of lizards, and significant improvements to taxonomic identification of arvicoline rodents.

Name thesis:degree_name

Doctor of Philosophy

Discipline thesis:degree_discipline

Environmental Studies (Geosciences)

Grantor

The University of Texas at Austin

Year dc:date.issued

2024

Author dc:creator

• Keenan Early, Erin Michaela

Advisor dc:contributor.advisor

• Shanahan, Timothy M.

Committee members dc:contributor.committeemember

• Kemp, Melissa
• Bell, Christopher J., 1966-
• Bennett, Philip C. (Philip Charles), 1959-
• Collins, Matthew J.

• GDGT
• brGDGT
• Paleotemperature proxy
• Paleoclimate proxy
• North America
• Quaternary
• Microtus
• Lizard
• Bacterial incubation
• Bacteria
• Phrynosomatidae
• Squamata
• Sceloporus
• Arvicolinae
• Cricetidae
• Arvicoline rodents
• Proteomics
• ZooMS
• Collagen peptide fingerprint
• Paleoproteomics

Language dc:language.iso

English

Identifier URI

https://doi.org/10.26153/tsw/62867

OAI identifier oai:identifier

oai:repositories.lib.utexas.edu:2152/135547