H₂S exposure elicits differential expression of candidate genes in fish adapted to sulfidic and non-sulfidic environments

Disentangling the effects of plasticity, genetic variation, and their interactions on organismal responses to environmental stressors is a key objective in ecological physiology. We quantified the expression of five candidate genes in response to hydrogen sulfide (H₂S) exposure in fish (Poecilia mexicana, Poeciliidae) from a naturally sulfide-rich environment as well as an ancestral, non-sulfidic population to test for constitutive and environmentally dependent population differences in gene expression patterns. Common garden raised individuals that had never encountered environmental H₂S during their lifetime were subjected to short or long term H₂S exposure treatments or respective non-sulfidic controls. The expression of genes involved in responses to H₂S toxicity (cytochrome c oxidase, vascular endothelial growth factor, and cytochrome P450-2J6), H₂S detoxification (sulfide:quinone oxidoreductase), and endogenous H₂S production (cystathionine γ lyase) was determined in both gill and liver tissues by real time PCR. The results indicated complex changes in expression patterns that - depending on the gene - not only differed between organs and populations, but also on the type of H₂S exposure. Populations differences, both constitutive and H₂S exposure dependent (i.e., plastic), in gene expression were particularly evident for sulfide:quinone oxidoreductase, vascular endothelial growth factor, and to a lesser degree for cytochrome P450-2J6. Our study uncovered putatively adaptive modifications in gene regulation that parallel previously documented adaptive changes in phenotypic traits.