Elli
e Tushar
Advisor: Dr. Gregory Ragland
Date: April 24, 2026
Time: 12:00pm - 1:00pm
Location: North Classroom 1003
Evolutionary Divergence and Thermal Plasticity: Investigating Transcriptional Responses in Tropical and Temperate Drosophila Species.
Phenotypic plasticity enables organisms to adjust to environmental variation, yet it remains unclear how plastic responses evolve across macroevolutionary timescales. While microevolutionary studies suggest that selection can refine, enhance, or suppress plasticity, it is unknown whether these patterns persist across deeply divergent taxa. Here, I used a comparative transcriptomic approach to examine thermal plasticity across eight Drosophila species representing both tropical and temperate lineages. Adult males were exposed to cold (10 °C) and control (21 °C) conditions, and RNA sequencing was used to quantify genome-wide gene expression responses. Across all species, cold exposure induced widespread transcriptional plasticity, with thousands of genes differentially expressed. However, both the magnitude and direction of gene expression changes were remarkably similar across species groups, with strong positive correlations in log fold changes despite evolutionary divergence of ~40–50 million years. These results support a hypothesis of evolutionary stasis in transcriptomic plasticity, consistent with constraint or stabilizing selection maintaining conserved responses across lineages. Functional enrichment analyses revealed shared upregulation of genes involved in cuticle formation and energy metabolism, suggesting common physiological responses to cold stress. In contrast, one species, Drosophila montana exhibited a distinct, muted transcriptional response, potentially reflecting a diapause state rather than acute transcriptional plasticity. Additionally, genes with complex evolutionary histories (non-1:1 orthologs) showed greater plasticity than conserved genes, indicating that evolutionary flexibility influences transcriptional responsiveness. Together, these findings suggest that while plasticity is widespread across the transcriptome, it does not necessarily diverge across macroevolutionary timescales, highlighting the role of constraint, shared ancestry, and alternative physiological strategies in shaping transcriptomic responses to environmental stress.