Meeting Abstract
Under environmental stress, organisms may adopt two strategies to allow for maintenance of organismal function: regulation, in which organisms actively regulate internal concentrations of a substance to maintain homeostasis, or conformity, in which internal concentrations of a substance match that of the environment. Hydrogen sulfide (H2S) environments provide a unique opportunity to test how these strategies may facilitate adaptation to harsh environments because the candidate pathways for both conformity (modification of toxicity targets) and regulation (modification of detoxification enzymes) are known. H2S is a respiratory toxicant that inhibits cytochrome c oxidase (COX), which halts aerobic ATP production, and is regulated by the sulfide:quinone oxidoreductase (SQR) pathway. Despite the toxicity, populations of Poecilia mexicana are known to inhabit sulfidic and non-sulfidic streams in replicated river drainages. This replication provides an opportunity to compare mechanisms of adaptation in response to a single source of selection. Genomic data indicates evidence for conformity (evolution of a sulfide-resistant COX) and regulation (increased gene expression of the SQR pathway), but the importance of either mechanism likely varies among populations. If fish are regulators, tolerant and non-tolerant populations should differ in the threshold at which maintenance of homeostasis fails, but if they are conformers, they should differ in the endogenous concentration of sulfide that results in loss of organismal function. To measure mechanisms of sulfide tolerance, I utilized mitoA, a molecular probe that binds H2S in the mitochondria, to determine how internal sulfide concentrations scale upon exposure to environmental H2S across different tissues in two population pairs of P. mexicana. This approach allows us to functionally test alternative hypotheses generated from next generation sequencing data.
