Hidden markers of health: how mercury affects gene expression in developing seabirds

Mercury is a globally recognized environmental contaminant that bioaccumulates and biomagnifies in food webs, thereby causing adverse health effects in both humans and wildlife. While mercury exposure is known to impact several life-history traits in birds, the molecular mechanisms underlying these effects remain poorly investigated. In this study, we examined the association between blood mercury concentrations and the expression of 15 key genes involved in detoxification and oxidative stress regulation in magnificent frigatebird Fregata magnificens chicks from French Guiana. Specifically, we measured the expression of genes encoding glutathione-dependent enzymes (GSTA1, GSTA2, GSTK1, GSTM1, GSTT1_0, GSTT1_1, GPX1, GPX2, GPX3, GSS, GSR_0 and GSR_1), thioredoxin system (TXNRD1 and TXNRD3), and metallothionein (MT1). Our results revealed a significant decrease in GSTA1, GSTA2, and GSTT1_1 expression with increasing mercury concentrations. No significant associations were found for glutathione peroxidases, glutathione synthetase and reductases, thioredoxin reductases, or metallothionein expression. These findings might indicate a potential increase in toxicity and cellular damage due to the lower detoxification of glutathione S-transferases. We emphasize the need for further investigations into species-specific mechanisms of detoxification. Our study supports the utility of gene expression analysis in addition to traditional physiological measurements to assess contaminant induced disruptions.