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Dryad

Reduced fitness associated with introgression within the Western Mediterranean admixed population of European seabass

Abstract

Unraveling hybridization consequences on fitness is of main concern in ecology and evolution. Many studies report how evolutionary mechanisms modulate the mosaic of introgression within genomes but few assessed the associated effect of admixture on fitness traits.

The Western Mediterranean population of the European seabass (Dicentrarchus labrax) results from hybridization between the Atlantic and the Mediterranean lineage in the Alboran Sea. By genotyping 1850 admixed fish, we assessed the relationship between individual admixture levels and fitness traits in different thermal regimes (19°C, 21°C and 23°C). Admixed individuals with more Atlantic ancestry displayed a biased sex ratio toward males, and were more sensitive to temperature variation. Additionally, they also had a lower body weight (which is correlated to fecundity in fish), compared to fish with less Atlantic ancestry. Atlantic ancestry is disadvantageous in the Mediterranean basin which is consistent with the previously observed purging of Atlantic ancestry tracts following hybridization.