Courtney Passow

Local adaptation in extremophile fish

​

Extremophiles are organisms with the ability to survive in environments characterized by strong physicochemical stressors lethal to most other organisms, providing excellent models to further our understanding of life’s capacities and limitations to deal with far-from-average conditions. To address this, my graduate research focused on identifying variation in physiological processes among fish residing in starkly different environmental conditions to understand how organisms cope with extreme environments and disentangle the roles of short-term plastic responses and evolved population differences. 

        For my graduate research under the guidance of Dr. Michael Tobler, I used Poecilia mexicana, a series of extremophile fish populations that has colonized toxic hydrogen sulfide (H2S) rich springs and caves, to address three major objectives: (1) Investigate energetic consequences of life in extreme environments and test whether predicted reductions in organismal energy demands evolved repeatedly along replicated environmental gradients. (2) Characterize variation in gene expression among populations and organs to test for interactive effects between different stressors and identify potential physiological mechanisms underlying adaptation to H2S and cave environments. (3) Conduct a common garden and H2S-exposure experiments to test how evolutionary change and plasticity interact to shape variation in gene expression observed in nature. To address this, I focused on measuring metabolic physiology and modifications of physiological processes by quantifying changes in gene expression in fish adapted to the presence or absence of H2S or light.

​

​

Integrating gene co-expression networks and genomic divergence across cave and surface morphs

​

Adaptation by natural selection is a key generator of biodiversity. In particular, variable environments can drive local adaptation and diversification of complex phenotypes. Local adaptation typically involves modification of morphological, behavioral, biochemical or physiological traits mediating an increase in fitness under specific environmental conditions. Nonetheless, understanding the effect of local adaptation on gene interactions and ultimately linking genotype, phenotype, and fitness remains a major challenge.

       To address this, in my postdoctoral research I plan to investigate how organisms adapt to nutrient and light-poor cave environments. In particular, I will utilize new technological and theoretical tools to identify changes in gene co-expression networks between cave and surface populations and test whether divergent co-expressed nodes are also under direct selection. I will be conducting this research in collaboration with Dr. Suzanne McGaugh (Department of Ecology, Evolution and Behavior, University of Minnesota) and Dr. Peter Tiffin (Department of Plant Biology, University of Minnesota).

​

​

​

​