Keywords

transcriptome selection plasticity adaptation gene expression

Abstract

Anurans (frogs) are spectacularly diverse in their life histories, evolutionary trajectories, and morphological features. Advancement of next-generation sequencing techniques has improved knowledge of anuran genetics, but the functional genomic underpinnings of adaptation in most frog species remains uncharacterized. Transcriptomic approaches are some of the most powerful tools available to understand the molecular workings of adaptation among lineages and species. Because anurans face a multitude of anthropogenic threats and are unique in their biphasic life history, a question of particular interest is how gene expression profiles relate to phenotypic variation within and among species. In this dissertation, I tackle this question at multiple biological scales ranging from individuals to populations to species. I investigate transcriptome expression profiles and sequence data across the anuran tree of life, with an emphasis on non-model frog species native to the Americas. My overarching aim is to provide novel insights into how transcriptome elements recapitulate phenotypic adaptation in anurans. In Chapter 1, I identify unique signals of positive selection on putative adaptation genes related to high-elevation diversification in Pristimantis, a species-rich frog complex that undergoes direct development. I found prevalent relaxed purifying selection among single-copy genes, while intensified positive selection occurred more in duplicated genes. Overall, my results suggest that these genes possess distinct properties in Pristimantis species and are potential targets for future molecular studies of high-elevation adaptation and direct development. Chapter 2 features a fully factorial manipulation experiment using Rana pipiens tadpoles to explore the impact of environmental predator cues and exposure to the pathogenic fungus Batrachochytrium dendrobatidis (Bd) on tadpole morphology and early development gene expression. Although significant effects of pathogen introduction on tadpole mortality were observed, no significant impacts on tadpole morphology resulted from Bd or predator cues. Negative Bd swab results at the end of the experiment may indicate that tadpoles’ ability to clear the pathogen can offset effects on tadpole mouthpart morphology during early development. While my experiment did not yield plasticity results suitable for gene expression analysis, methods and analyses may offer valuable context for future studies of plasticity gene expression. In Chapter 3, I analyze transcriptomic data from natural populations of Rana yavapaiensis frogs threatened by chytridiomycosis to discern individual and population-level differences in gene expression. I found that tolerant populations exhibit stronger suppression of genes that negatively regulate transcriptional responses to chytrid infection compared to susceptible populations. Altogether, my dissertation integrates molecular insights into species evolution, environmental challenges, and pathogen responses, illustrating the dynamic resilience of frogs in a changing world.

Completion Date

2024

Semester

Summer

Committee Chair

Anna E. Savage

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Biology

Degree Program

Integrative and Conservation Biology

Format

application/pdf

Release Date

8-15-2024

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

Campus Location

Orlando (Main) Campus

Accessibility Status

Meets minimum standards for ETDs/HUTs

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