ORCID Identifier(s)

0009-0003-7129-9695

Graduation Semester and Year

Summer 2026

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Quantitative Biology

Department

Biology

First Advisor

Matthew Fujita

Second Advisor

JC Buckner

Third Advisor

Todd Castoe

Fourth Advisor

Jeffery Demuth

Fifth Advisor

Matthew Walsh

Abstract

Animals inhabit a world saturated with chemical information. Long before the evolution of eyes or ears, the earliest organisms detected and responded to molecules in their surroundings, and chemical sensing remains the most phylogenetically widespread and evolutionarily ancient sensory modality across the tree of life. Among terrestrial vertebrates, squamate reptiles—lizards and snakes—have elaborated chemical communication to a remarkable degree, relying on chemosensory cues to mediate nearly every facet of their social and ecological lives. Central to this reliance, in many lizard lineages, are specialized epidermal secretory organs that synthesize and release complex semiochemical blends onto the substrate and the body surface. These glands, and the molecular machinery that builds and operates them, are the subject of this dissertation.

Despite more than a century of morphological, histological, behavioral, and biochemical attention to lizard chemical glands, the gene regulatory architecture that underlies their development, secretion, and evolutionary diversification has remained almost entirely unexplored. This is a conspicuous gap. The chemistry of gland secretions has been documented in elegant experimental detail, and the macroevolutionary distributions of glands across the squamate tree has been mapped at continental and global scales; yet, we have lacked a molecular, systems-level account of how these organs are constructed and how that construction has been modified over evolutionary time. The work presented here was designed to help fill that gap by bringing comparative transcriptomics, gene co-expression network analysis, and phylogenetic comparative methods to bear on the evolution of chemically active epidermal glands in lizards.

This dissertation comprises one introductory chapter and three empirical chapters, each addressing the evolution of glandular chemical signaling at a different phylogenetic and conceptual scale. The first empirical chapter (Chapter 2) examines femoral gland gene regulation within a single genus, the whiptail lizards (Aspidoscelis), and asks how a complex signaling trait is maintained across one of the most striking transitions in vertebrate biology: the shift from sexual reproduction to obligate parthenogenesis. By assembling a femoral gland transcriptome atlas and applying differential expression and weighted gene co-expression network analyses across sexual and asexual lineages, this chapter tests whether signaling divergence reflects wholesale regulatory rewiring or instead the quantitative modulation of deeply conserved networks—what François Jacob (1977) famously termed evolutionary tinkering. The second empirical chapter (Chapter 3) broadens that lens to the whole of non-ophidian Squamata, using comparative transcriptomics spanning fifteen genera and seven families to test whether the two principal histological classes of lizard epidermal glands—follicular glands and generation glands—share a conserved molecular foundation consistent with deep homology, or whether they represent independent evolutionary inventions. The third empirical chapter (Chapter 4) narrows again, this time onto the South American iguanian family Tropiduridae, to ask how the abiotic environment shapes the generation gland secretome across one of the most ecologically diverse open-habitat lizard radiations on Earth.

The introductory chapter (Chapter 1) provides the conceptual and technical foundations for those three studies. It begins with the broad biology of chemical communication in animals, then narrows to the chemosensory world of squamate reptiles, the morphology and histology of their epidermal glands, and the chemistry of the secretions those glands produce. It next develops the two evolutionary frameworks that recur throughout the dissertation—deep homology and evolutionary tinkering—before introducing the two focal study systems, Aspidoscelis and Tropiduridae, in detail. The introduction closes by stating the overarching objectives and hypotheses that unify this dissertation.

Keywords

Chemical communication, Femoral glands, Comparative transcriptomics, Gene co-expression networks, Deep homology, Lizard, Parthenogenesis, Tropiduridae, Evolutionary tinkering

Disciplines

Behavior and Ethology | Bioinformatics | Evolution | Genomics

License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

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Available for download on Thursday, August 05, 2027

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