Hydrogen sulphide sensitivity and tolerance in genetically distinct lineages of a selfing mangrove fish (Kryptolebias marmoratus).

Mangroves are critical marine habitats. High hydrogen sulphide (HS) is a feature of these important ecosystems and its toxicity creates a challenge for mangrove inhabitants. The mangrove rivulus (Kryptolebias marmoratus) is a selfing, hermaphroditic, amphibious fish that can survive exposure to 1116 μM HS in the wild. These fish rely on cutaneous respiration for gas and ion exchange when emerged. We hypothesized that the skin surface is fundamentally important in HS tolerance in these mangrove fish by limiting HS permeability. To test our hypothesis, we first disrupted the skin surface in one isogenic lineage and measured HS tolerance and sensitivity. We increased water HS concentration until emersion as a measure of the ability to sense and react to HS, which we refer to as sensitivity. We then determined HS tolerance by preventing emersion and increasing HS until loss of equilibrium (LOE). The HS concentration at emersion and LOE were significantly affected by disrupting the skin surface, providing support that the skin is involved in limiting HS permeability. Capitalizing on their unique reproductive strategy, we used three distinct isogenic lineages to test the hypothesis that there would be genetic differences in HS sensitivity and tolerance. We found significant differences in emersion concentration only among lineages, suggesting a genetic component to HS sensitivity but not tolerance. Our study also demonstrated that external skin modifications and avoidance behaviours are two distinct strategies used to tolerate ecologically relevant HS concentrations and likely facilitate survival in challenging mangrove habitats.