Much of our research focuses on understanding the evolution of phenotypic flexibility and mechanisms underlying flexible responses to changing environmental conditions, drawing on techniques from ecophysiology and genomics.
Environmental Drivers of Variation in Phenotypic Flexibility
Phenotypic flexibility refers to the ability of an organism to reversibly change its trait value throughout its life. Theory predicts that the relative degree of flexibility exhibited by a population will positively correlate with the environmental heterogeneity they experience, yet there are few empirical examples to support this. Maria combined field studies and manipulative experiments in the lab in order to characterize the role of temperature heterogeneity as a driver of variation in flexibility among individuals. This work is centered on a common North American songbird, the Dark-eyed Junco (Junco hyemalis), and its relatives. She performed in situ physiological measurements of juncos across the country, range-wide population genetic assays, and acclimation studies replicated on several Junco populations. The findings from this work are important for understanding large-scale physiological patterns, local adaptation, and potential responses to future environmental change.
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The Architecture of Phenotypic Flexibility within a Complex Trait
A system’s capacity for flexibility may be determined by its underlying trait architecture, and these relationships can have important implications for both organismal adaptation and the evolvability of acclimatization responses. To explore the mechanistic basis of phenotypic flexibility in complex traits, Maria used in-depth physiological assays to assess how relationships among traits vary as the environmental context changes, as well as which trait adjustments are required to support flexibility in whole-organism performance. Our results suggest that simple and reversible modifications can significantly impact whole-organism performance, and thus that the evolution of phenotypic flexibility in a single component part could impart flexibility for the entire system.
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Avian Transcriptomic Responses Underlying Flexibility
At a mechanistic level, individuals adjust phenotypic expression across the year through the dynamic responses of the transcriptome to changes in the environment. The details of these transcriptomic responses are only just starting to be explored in wild birds. We identify the regulatory mechanisms that juncos use to respond to seasonal challenges by combining functional physiological assays and gene expression data. We've used these techniques (1) to characterize the influence of photoperiod and temperature cues on junco flexibility, (2) to test hypotheses about the contributions of shivering and non-shivering thermogenesis to junco body temperature maintenance in the cold, and, more recently, (3) to look for concerted responses to seasonal cues across songbird species.
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The Relative Roles of Heat Production and Conservation in the Cold
Maintaining a relatively stable body temperature is key to endothermic homeostasis and survival. Seasonal climates necessitate changes by small endotherms in endogenous heat production and heat dissipation in order to mediate fluctuations in their thermal environment throughout the year. Maria used acclimation studies to understand the contribution of these two complimentary processes for endothermic body temperature maintenance. By combining assays of shivering capacity, thermal conductance of the skin and plumage (i.e., heat loss to the environment), and body temperature in acute cold trials, our findings both demonstrate the ability of birds to adjust their thermoregulatory strategies in response to thermal cues and reveal that birds may combine multiple responses to meet the specific demands of their environments. Lab members are now quantifying properties of the feathers to determine how conductance is altered.
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Connecting measures of physiological performance with social foraging behavior and survival
Maintaining a high shivering capacity may confer advantages under some conditions, but likely also comes with high energetic costs that require increased food intake. During winter, when resources may be scarce, these increased energetic demands may be difficult to meet. We are employing specialized bird feeders that use ultra high frequency radio frequency identification (RFID) to log visits of marked individuals for which we are performing detailed physiological assays. We are using this technology for two projects: (1) Together with Dai Shizuka, we are exploring interactions between social foraging behavior and physiology within winter mixed-species flocks; and (2) Exploring tradeoffs between thermogenic demands and resource acquisition in the winter using foraging rates and survival estimates.
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Collaborators
Matt Carling (U. Wyoming) - We are exploring tradeoffs between parasite prevalence and metabolic performance in juncos
Zac Cheviron (U. Montana) - Zac was Maria's graduate advisor and a collaborator on much of the above work
Nate Senner (UMass Amherst) - Nate and Maria have investigated interactions between ecological and physiological processes in empirical and theoretical systems
Dai Shizuka (U. Nebraska Lincoln) - We have an NSF grant looking at interactions between physiology & social foraging behavior
John Stager (Maria's dad) - A professional tinkerer turned robot builder, also the brains behind our new RFID feeders
Dave Swanson (U. South Dakota) - Dave and Maria have collaborated on a number of junco physiology projects
Scott Taylor (CU Boulder) - Scott & Maria are investigating the genomic basis of individual differences in physiological flexibility
Matt Carling (U. Wyoming) - We are exploring tradeoffs between parasite prevalence and metabolic performance in juncos
Zac Cheviron (U. Montana) - Zac was Maria's graduate advisor and a collaborator on much of the above work
Nate Senner (UMass Amherst) - Nate and Maria have investigated interactions between ecological and physiological processes in empirical and theoretical systems
Dai Shizuka (U. Nebraska Lincoln) - We have an NSF grant looking at interactions between physiology & social foraging behavior
John Stager (Maria's dad) - A professional tinkerer turned robot builder, also the brains behind our new RFID feeders
Dave Swanson (U. South Dakota) - Dave and Maria have collaborated on a number of junco physiology projects
Scott Taylor (CU Boulder) - Scott & Maria are investigating the genomic basis of individual differences in physiological flexibility