Cytogenetic studies in North American minnows(Cyprinidae). XVIII. Chromosomal NOR variation among eight species.

Abstract

The karyotypes and chromosomal nucleolus organizer region or NOR phenotypes of eight species of North American cyprinid fishes are documented. All eight species possessed 2n=50 chromosomes. Four species (Cyprinella formosa, Cyprinella gibbsi, Notropis boops, and Notropis dorsalis) possessed only a single pair of NOR-bearing chromosomes, whereas four species (Notropis petersoni, Notropis sabinae, Phenacobius mirabilis, and Semotilus atromaculatus) possessed multiple NORs, i. e., more than one pair. The phylogenetic implications of the chromosomal NOR data in the eight species are discussed relative to current concepts of North American cyprinid systematics based largely on morphological data. A phylogenetic hypothesis based on chromosomal NOR and other data is presented for 11 species of the cyprinid genus Cyprinella, and our previous hypothesis that a single pair of NOR chromosomes is the plesiomorphic NOR state for a large eastern North American cyprinid lineage is questioned.