Research & Projects

In endotherms, body size is expected to decrease in response to climate warming as a modern extension of Bergmann’s rule. This rule predicts body size increases with latitude because larger individuals have more efficient heat retention in cold environments but are less able to dissipate heat in warm environments. When phenotypic traits are sensitive to the same hormonal mechanisms, changes in hormone levels are predicted to facilitate rapid phenotypic responses to changing environmental conditions. One hormonal mechanism that is well-positioned to regulate rapid phenotypic change is insulin-like growth factor 1 (IGF-1). IGF-1 is a protein hormone that influences growth rate and body size across varying environments. Specifically, IGF-1 is sensitive to a range of environmental stimuli including nutrient availability and temperature, both predicted to vary with latitude. Thus, IGF-1 is likely a key mechanism influencing body size and other life-history traits via micro-evolutionary changes, phenotypic plasticity, or both. To determine if IGF-1 promotes differences in growth and body size across different latitudes as part of Dr. Britt Heidingers NSF research project, we explored the natural variation in plasma IGF-1 in free-living adult and 10-day-old nestling house sparrows (Passer domesticus) along a latitudinal gradient across the United States. 

Wild songbirds are an excellent model for studying the costs and benefits of parental care, as most species express some level of biparental care. In general, female songbirds typically devote more effort to parental care than males, but this differs as a function of ecology. For example, paternal investment tends to increase with decreasing latitude. Males living closer to or in the tropics are observed to increased investment compared to temperate males, assisting in incubation and brooding behaviors, something rarely seen in songbirds in the North-Temperate zone. Despite well-established patterns of increasing paternal care with decreasing latitude across species, we do not know if these patterns will hold within species, and the mechanisms influencing these patterns are still poorly understood. For my postdoc, I wrote and received an NSF Postdoctoral Research Fellowship in Biology to explore how the mechanisms of house sparrows (Passer domesticus) paternal care vary with ecological condition across a latitudinal gradient in North America.

Urbanization is the leading cause of species loss and habitat change in North America. As human populations continue to spread, understanding the impacts of urbanization on wild animals is increasingly urgent. My doctoral research used an integrative approach to develop a broad understanding of how urbanization affects the physiology, behavior, and fitness of breeding song sparrows (Melospiza melodia). 

A species first response to rapid environmental change is often to change behavioral phenotypes. For instance, urban male song sparrows are more territorially aggressive compared to rural males. This is not uncommon, but we do not understand the behavioral trade-offs associated with this elevated aggression, the consequences on their mates and offspring, nor the mechanisms associated with subsisting in urban environments. I found that, surprisingly, the more aggressive urban males maintained elevated parental care and urban song sparrows had higher reproductive success across all five years compared to rural song sparrows. 

As a continuation of this research, I explored the physiological mechanisms of behavioral recovery in urban dwelling animals. The glucocorticoid (corticosterone in birds, or cort) stress response is one physiological mechanism that may allow animals to maintain breeding behaviors despite the novel stressors imposed by urban habitats. Urban males and females had lower circulating corticosterone levels at baseline and stress induced compared to rural and had lower hippocampal expression of glucocorticoid receptors and the regulatory enzyme 11β-HSD2 compared to rural song sparrows. Thus, these results suggest that urbanization dulls the hormonal stress response. Finally, urban birds had significantly higher fitness metrics compared to rural birds, despite significantly higher levels of brood parasitism in urban habitats. Therefore, individuals who settle in disturbed environments may be of higher quality and/or benefit from the ecological conditions of urban habitats to achieve higher fitness.