Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

Brent L. Lockwood


Rapidly changing climate conditions, including extreme temperature events, have wide-reaching implications for organismal adaptation. Organisms with complex life cycles can be differentially susceptible to physiological challenges posed by acute temperature stressors depending on developmental stage. Thus, sensitive life stages may act as a selective sieve through which species are differentially able to persist in a changing, warming world. Terrestrial ectotherms, such as the cosmopolitan Drosophila melanogaster, are dependent upon their external environment to dictate internal body temperature. The non-motile D. melanogaster embryo is entirely reliant upon innate physiological defense mechanisms to protect against and respond to the damaging effects of heat stress, given the inability to behaviorally thermoregulate. Early embryos (0-2 hours post fertilization) have been shown to display substantial differences in thermal tolerance between regionally distinct tropical and temperate populations. The rapid local adaptation seen in this trait is indicative of strong selection for the underlying favorable alleles. However, the underlying genetic basis of embryonic thermal tolerance is previously unknown. Previously, our lab used whole genome quantitative trait locus (QTL) mapping via a repeated backcrossing design to identify the genomic basis of differential embryonic thermal tolerance between flies of tropical vs. temperate origin. To determine the extent to which gene regulatory variation underlies embryonic thermal tolerance, I measured transcriptomic responses to heat stress using the same tropical, temperate, and advanced introgression lines that were used in the QTL mapping study.

I identify 212 differentially expressed genes between the three genotypes (tropical, temperate, introgression) and 650 differently expressed genes between the two temperature treatments (25°C, 34°C). Additionally, I identify gene clusters containing a total of 985 genes that were significantly associated with response to heat stress, and one gene cluster containing a total of 52 genes that were significantly associated with LT50. Functional analysis of these differentially expressed genes and clusters indicates that precise regulation of aerobic metabolism and oxidative phosphorylation is instrumental in reducing cellular damage accrued due to the formation of reactive oxygen species (ROS) by downregulating processes that lead to ROS formation. I observe a strongly conserved heat shock response to the stressful treatment temperature amongst all genotypes, including upregulation of protective elements and some metabolic downregulation. The most prominent finding, supported by the list of genes containing polymorphisms in different allelic frequencies between temperate and introgression genotypes, was the difference in magnitude and depth of the downregulation of metabolic systems in more thermally tolerant embryos. In addition to reduction of catabolic activity, more nuanced regulation of transcriptional machinery and the formation subcellular nucleoprotein complexes appear to be plastic mechanisms contributing to the divergence in thermal tolerance between locally adapted regional genotypes.



Number of Pages

103 p.

Available for download on Tuesday, April 22, 2025