Author ORCID Identifier
Document Type
Dissertation
Date of Award
2026
Degree Name
Doctor of Philosophy (PhD)
Department
Biology
First Advisor
David L Swanson
Abstract
Animals in temperate regions are facing changing environmental conditions. Superimposed on warming temperatures is an increase in environmental variability and frequency of extreme weather events. Small temperate birds are highly flexible, with metabolic rates that increase during prolonged exposure to cold winter temperatures. However, the underlying mechanisms of this flexibility, and the potential impacts of climate change, are incompletely known. In the first three chapters of this dissertation, I explore the potential impacts of fluctuating cold temperatures on house sparrows (Passer domesticus). This species is well-studied, has a broad global range, and has populations that remain in South Dakota all year, making them a model for studying responses to environmental change. In my first two chapters, I exposed birds to warm, stable cold, or fluctuating cold conditions for six weeks and measured effects on metabolism. I found that organismal-level changes such as summit metabolic rate, a measure of cold tolerance, did not differ between stable cold and fluctuating cold temperature treatments. This suggests that increased temperature variability may not prevent the maintenance of a winter phenotype in small birds. However, fluctuating cold conditions did result in differences in liver mass and in enzymes related to fat transport, indicating a physiological response to unpredictable conditions. In my third chapter, I assessed whole genome DNA methylation, an epigenetic marker that can modify gene expression. DNA methylation patterns differed between warm and cold treatments and further varied between stable cold and fluctuating cold treatments. This provides evidence that epigenetic modifications are associated with seasonal phenotypic flexibility in small birds. In my last chapter, I explored the potential impact of winter seasonal acclimatization on immune function in American goldfinch (Spinus tristus), another small passerine that remains in South Dakota all year. I measured microbicidal capacity of serum samples collected in summer and winter to determine whether winter temperatures result in immune suppression. I found seasonal differences in fungicidal and bactericidal capacity, but not an overall winter decrease. From these results, I hypothesize that goldfinch modulate different aspects of immune function to match seasonal environmental risks, such as higher fungal activity in the summer.
Subject Categories
Biology | Biomedical Informatics | Physiology
Keywords
Birds, DNA methylation, Ecophysiology, Metabolism, Phenotypic flexibility
Number of Pages
96
Publisher
University of South Dakota
Recommended Citation
Marolf, Chelsi J., "Effects of cold and fluctuating cold temperatures on metabolic flexibility, immune function, and epigenetic variation in small birds" (2026). Dissertations and Theses. 409.
https://red.library.usd.edu/diss-thesis/409