Metal stress-related gene expression patterns in two marine invertebrates, Hediste diversicolor (Annelida, Polychaeta) and Littorina littorea (Mollusca, Gastropoda), at a former mining site.

Abandoned mines often contaminate sediments with dissolved heavy metals and are known to impact many taxa. Physiological responses needed to avoid oxidative stress from metal toxicity include the upregulation of detoxification and metal-binding proteins such as glutathione-s-transferases and metallothioneins, which have been studied in diverse species. Fewer studies, however, have focused on gene expression changes to better understand these molecular mechanisms, especially across multiple species at a single contaminated site. To this end, the purpose of this study was to characterize metal stress-related gene expression in two species from different phyla, Hediste diversicolor (Annelida, Polychaeta) and Littorina littorea (Mollusca, Gastropoda), at a former mine site (Callahan Mine, Maine, USA). Both species and sediments were collected from a mine-affected tidal estuary (Goose Pond) and a nearby reference site. Elevated sediment metal levels were confirmed at Goose Pond. H. diversicolor individuals weighed significantly less at Goose Pond, while L. littorea weighed similarly at both sites. Transcript levels were stable in H. diversicolor but weakly upregulated in L. littorea, which likely reflect the importance of other physiological strategies for metal sequestration, or variable metal exposure at the individual level, respectively. In addition, patterns in glutathione-s-transferase expression differed across isoforms in H. diversicolor, while L. littorea exhibited divergent expression patterns in foot muscle and hepatopancreas. Overall, these results reinforce that diverse species likely undergo different physiological responses to metal toxicity, and more research is needed to investigate these mechanisms.