Abstracts (first author)
Genetic structure, selection and duplication in European eels MHC class II genesPDF
Understanding adaptation and selection in populations facing environmental changes is a major concern. Our project aims to understand the adaptation and resilience of endangered catadromous European eel to increasing parasitic pressure. Anguilla anguilla has encountered successive waves of exotic invasive parasites, namely, the swimbladder nematode Anguillicoloides crassus. Infested individuals have high swimming performance costs; and might fail to complete the reproductive migration back to the Sargasso Sea. Prevalence of such parasites is much higher in the naive European populations compared to native Japanese hosts. However, the nature of the ongoing adaptation and impact on eel’s biology remain largely unknown. Given the role of Major Histocompatibility Complex (MHC) genes in host–parasite interactions, we designed specific primers to sequence 2 class II exons. Using NGS, we sampled alleles from 12 European populations (N = 120) collected throughout the species distribution range, as well as from one American population (N=10). Additional historical samples (1874) from Charente were included. Our results indicate success in isolating relevant MHC class II genes; we identified respectively 149 and 154 DAA and DAB MHC class II alleles. The multiple copy nature of the MHC loci was confirmed, with at least 4 and 5 gene copies for DAA and DAB loci, respectively. European and American eels were found to share the same allelic pool, a result in sharp contrast with microsatellite data, suggesting that balancing selection is acting on these genes while ancient polymorphisms is retained within the Atlantic lineages. There was no evidence for temporally fluctuating selection pressure. Finally, the eel MHC class II exons appeared to be under positive selection and at the upper range of rho and omega values in teleosts. These results suggest that recent duplications occurred in the genus that might have facilitated inter-locus recombination and high allelic diversity.