Footprints of Natural Selection in North Atlantic Eels: A Review

Abstract

The study of natural selection and local adaptation is a thriving field of research. Local adaptation is driven by environment components and results in locally adapted phenotypes with higher fitness relative to other phenotypes from other locations in the species range. Tests of local adaptations have traditionally been done using transplant experiments, but the advent of next-generation sequencing methods have allowed the study of local adaptation to move from a phenotypic to a genomic approach. By using genome scans and state-of-the-art statistical tests, researchers can identify genes putatively under selection and study the genomic architecture of local adaptation, which often includes the observation of clustering of adaptive genes concentrated in fewer genomic regions known as “genomic islands of divergence”. The two species of North Atlantic eels, the European and the American eel, are excellent species for studying selection since they are panmictic and present large population sizes, show a wide distribution range across extremely heterogenous environments, and are subject to high mortalities. We reviewed studies of natural selection and local adaptation in American eel, European eel, between life cycle stages, between European and American eel. Finally, we discussed genome architecture in relation to local adaptation in eels and the role of both genetic (i.e., local adaptation) and non-genetic (i.e., phenotypic plasticity) in the survival of eels across their distribution range.

Panmixia in the American eel extends to its tropical range of distribution: Biological implications and policymaking challenges

“…Phenotype, life history, and behavior of American eel changes with both latitude and habitat (Cairns et al., 2008; Jessop, 2010; Laflamme et al., 2012). Confirmation of panmixia across the entire species' range suggests that within‐generation habituation to local conditions is driven by spatially varying selection (polygenic selection within each generation; Babin et al., 2017; Gagnaire et al., 2012; Laporte et al., 2016; Pavey et al., 2015; reviewed in Pujolar et al., 2022), epigenetic adaptation (Liu et al., 2022), and/or habitat choice (Mensinger et al., 2021), alone or in synergy. In the absence of a genetic basis for these local differences, it can be expected that for genotypically determined traits, American eel individuals will react similarly to environmental cues range‐wide.…”