Genetic differentiation and introgression between putative subspecies of <i>Leuciscus soufia</i> (Teleostei: Cyprinidae) of the region of the Mediterranean Alps

Abstract

Because of interspecific hybridization, there is considerable controversy over the taxonomic status of many members within the family Cyprinidae. In this study, morphological and genetic characters of Leuciscus soufia, a cyprinid fish of southern France and northern Italy, were examined to verify the existence of three subspecies. Leuciscus soufia agassizi differs from Leuciscus soufia multicellus in morphology, in heterozygosity at two diagnostic allozyme loci, and by distinct mitochondrial lineages. Leuciscus s. soufia is morphologically similar to L. s. agassizi but exhibits decreased enzymatic polymorphism. However, two specimens of L. s. soufia from the Var River were found to have mitochondria of the subspecies multicellus, while four Bevera River specimens of L. s. multicellus possessed the mitochondria of the subspecies agassizi. These data argue in favour of introgressive hybridization between L. s. soufia and L. s. multicellus, rejecting the hypothesis that an ancestral population was fragmented, generating three "subspecies" that retained the original polymorphism. We propose that L. s. soufia and L. s. agassizi be regrouped within the soufia subspecies. A calibrated molecular clock dates the separation of the remaining subspecies back to the Messinian (5 million years ago). Sea level fluctuations likely mediated their secondary contact and subsequent introgressive hybridization.