Adaptive evolution in extreme environments

Primary author: Kerry McGowan
Faculty sponsor: Joanna L. Kelley

Primary college/unit: Arts and Sciences
Campus: Pullman


Hydrogen sulfide (H2S) is a lethal gas for most organisms because it inhibits aerobic respiration. However, the fish Poecilia mexicana successfully colonized several springs with high H2S after migrating from nearby freshwater springs. There are known H2S-related changes in gene expression in P. mexicana, but the underlying regulatory changes that control them are unknown. We hypothesized the following: (1)Transcription factors (TFs), which bind to DNA and regulate gene expression, would vary in their expression in P. mexicana based on the presence/absence of H2S. (2)TFs would co-vary with the expression of genes involved in aerobic metabolism and H2S detoxification. We performed network analyses on gene expression data from wild-caught P. mexicana from freshwater and H2S springs and lab-reared individuals exposed to H2S. The network analyses clustered genes into modules based on their expression levels across different treatments, allowing us to draw conclusions regarding the connectivity of these biological networks. Several TFs clustered in one module that significantly correlated with habitat (freshwater versus H2S) in wild-caught P. mexicana. Several aerobic respiration-related genes significantly correlated with different springs, indicating P. mexicana may have evolved different strategies to adapt to H2S. These results indicate that H2S affects the regulation of genes involved in aerobic respiration. As aerobic respiration includes some of the most evolutionarily conserved metabolic pathways in animals, this testifies to the potential of H2S to drive adaptive evolution. Understanding H2S metabolism in these fish will help inform the use of H2S as a therapeutic to treat human conditions.