Genetic analysis of the American eel helps explain its decline

An interesting paper entitled ‘RAD Sequencing Highlights Polygenic Discrimination of Habitat Ecotypes in the Panmictic American Eel‘ was recently published in the journal Current Biology by Scott A. Pavey et al. (2015). This study has found that there are differences between eels that feed in freshwater and eels that feed in brackish environments that were previously thought to be genetically interchangeable. This study found consistent genetic differences that correlate with habitat ecotypes in the American eel. Despite panmixia, the American eel has ecotypes specific to rearing habitats and these ecotypes are genetically distinct.

American eel genetics
American Eels of the upper St. Lawrence grow slowly but attain larger sizes (top) compared with eels in coastal areas (bottom). Credit: Guy Verreault/Current Biology 2015

This study has found that there are differences between eels that feed in freshwater and eels that feed in brackish environments that were previously thought to be genetically interchangeable. Both freshwater and brackish American eels are the same species, but they vary in size and have very different growth rates and life spans. It’s been thought that glass eels can detect whether they’ve ended up in brackish or freshwater habitats and acclimate accordingly. But this new study suggests that eels are predisposed to survive in these environments, depending on what genes they inherited.
This may help explain why some conservation efforts to preserve the freshwater eel haven’t been successful, as more plentiful brackish eels cannot easily change their traits to survive in freshwater environments.

This new study used new sequencing technologies to screen the eel genome in 45,000 places. The analysis identified 99 genes that differ between freshwater and brackish eels, including those associated with growth rate, heart development, and smell. It’s unknown whether this type of genetic differentiation exists in other, non-eel marine species with high levels of phenotypic plasticity.

Read more here.