Extreme environments allow for the investigation of life's capacity and limitations to cope with far-from-average environmental conditions. Springs rich in hydrogen sulfide represent some of the most extreme freshwater environments, because hydrogen sulfide halts energy production in animal cells. Nonetheless, some fish have colonized sulfide springs throughout the Americas, and it remains unknown how they can tolerate conditions so toxic that most other organisms perish. This project will compare closely related populations that live in adjacent sulfidic or nonsulfidic habitats to identify differences in genetic, biochemical, and physiological traits that underlie tolerance to this noxious chemical. It involves the identification of genetic differences between hydrogen sulfide-tolerant and susceptible populations, particularly in genes associated with pathways affected by hydrogen sulfide toxicity or detoxification. In addition, the tolerance and the susceptibility of fish populations will be measured in the presence or absence of hydrogen sulfide. This project will yield new insights into mechanisms underlying physiological tolerance to hydrogen sulfide and the workings of animals in the presence of physiochemical stressors. Given hydrogen sulfide's role in cellular processes and disease formation, this also has implications for biomedical applications. This project provides training opportunities in integrative biology for participants at all levels of higher education. It will also contribute to science education and public outreach through the generation of an exhibit at a local zoo and the involvement of high school teachers that will generate lesson plans implementing next generation science education standards for K-12 education in STEM fields.
Leveraging knowledge from toxicological and biomedical studies, this project addresses hypotheses about mechanisms of physiological adaptation to naturally H2S-rich environments and focuses on components of and associated with the oxidative phosphorylation pathway (OXPHOS) in mitochondria. These components include targets of H2S toxicity as well as enzymes involved in H2S detoxification. It is predicted that focal components are modulated or modified in sulfide spring populations, such that individuals have an increased ability to withstand elevated H2S concentrations, an increased ability to detoxify H2S enzymatically, and an ability to maintain or even increase mitochondrial energy production by using H2S a substrate to fuel metabolism. Furthermore, it is anticipated that modification of OXPHOS components has occurred repeatedly across independent lineages that have colonized sulfide springs. To test these predictions, this project focuses on an established model system (Poecilia mexicana) for the investigation of H2S adaptation and has three major empirical components: (1) Characterization of transcriptional and coding variation in candidate genes by use of high-throughput sequencing techniques and subsequent validation of effects on protein concentrations and structure. (2) Quantification of functional consequences of transcriptional and coding variation for H2S detoxification and bioenergetics both in vitro and in vivo. (3) Comparison of gene sequence and expression variation across a dozen independent population pairs from sulfidic and non-sulfidic habitats to test for convergence.