Hybridization between the Cyprinid Fishes Luxilus albeolus, L. cornutus, and L. cerasinus with Comments on the Proposed Hybrid Origin of L. albeolus

Abstract

Allozyme electrophoresis, restriction endonuclease analysis of mitochondrial DNA (mtDNA), and principal component analysis (PCA) of scale counts were used to characterize hybridization between Luxilus cornutus and L. cerasinus at a single locality (Barbour Creek, James River drainage, southwestern Virginia). PCA provided some separation between these species and L. albeolus from allopatric populations; however, overlap among all three species prevented complete discrimination of these forms with morphological characters alone. Application of morphological and genetic characters diagnostic for L. cornutus and L. cerasinus identified many hybrids in Barbour Creek. Most were F,s (as indicated by heterozygous genotypes at all four diagnostic allozyme loci) and exhibited mtDNAs of L. cerasinus. These data were contrasted with other hybridizing species of the genus Luxilus, which showed more extensive introgression. In addition, one individual exhibited morphological and genetic characteristics consistent with its identification as L. albeolus, providing the first report of this species in the James River. These results do not refute or support the hypothesis of hybrid origin for L. albeolus but highlight the difficulty of discriminating among ancestral polymorphism, convergence, and past hybridization.