Epigenetic Modifications in Response to Mercury Exposure in Wild Birds: A Study of Differential Methylation Patterns in Wild Louisianian Bird Populations

Abstract

The purpose of this work was to address the question of the epigenetic consequences of environmental mercury exposure. The quality of an ecosystem can have widespread effects on the health of all organisms living in that environment. Heavy metals like mercury are naturally occurring but can also be introduced into ecosystems via anthropological activity such as industry and agriculture. Methylmercury is a particularly harmful heavy metal compound because of its high affinity to living tissues and its consequent ability to remain in organisms long after exposure even low concentration exposures of the compound. One of the mechanisms by which organisms respond to environmental stress such as mercury exposure is through cellular modifications to DNA methylation patterns that affect which genes are inhibited or expressed. Birds are good indicators of how factors such as heavy metal levels affect ecosystem quality and for this reason, I examined DNA methylation in 30 wild birds from sites near sources of anthropogenic mercury pollution. I wanted to know if relatively high or low blood mercury levels corresponded with differential gene expression and if so, which cellular pathways were implicated. Analyses revealed that immune pathways and apoptotic pathways were most commonly affected by level of mercury exposure. The presence of changes to these pathways could have important consequences for bird fitness, bird population health as well as the health of other organisms in the affected ecosystems because of their own response to mercury exposure and the downstream effects of changes in bird population.