Phenotypic and genotypic variability in the American eel

We have conducted the most comprehensive analysis of neutral genetic population structure to date in order to revisit the null hypothesis of panmixia in this American eel. We used these data to provide the first estimates of contemporary effective population size (Ne) and temporal variation in effective number of breeders (Nb). Then, we tested for statistical associations between temporal variation in the North Atlantic Oscillation (NAO) index, effective number of breeders as well as two indices of recruit abundance. A total of 2142 eels from 32 sampling locations were genotyped with 18 microsatellite loci. We have confirmed that the panmixia hypothesis should be definitely accepted for this species. The effective population size Ne was estimated to be around 22 382 and relative abundance between cohorts varied from 473 to 10999. This study also showed that genetically based demographic indices can be used as surrogates for the abundance of breeders and recruits, which were both shown to be positively correlated to high (positive) phases of the NAO. Thus, long term genetic monitoring of American glass eels at several sites would represent a powerful and efficient complement to census monitoring in order to track demographic fluctuations and better understand their causes.