Chromosomal nor Karyotypes and Genome Sizes in Dionda (Osteichthyes: Cyprinidae) from Texas and New Mexico

Abstract

Chromosome numbers, chromosomal nucleolar organizer egion (NOR) phenotypes, and genome sizes (DNA contents) were documented for all nominal members of the North American cyprinid genus Dionda inhabiting Texas and New Mexico. All examined taxa, including four members of the Dionda episcopa complex (D. episcopa, D. argentosa, D. serena, and an undescribed species inhabiting the Colorado and Guadalupe river drainages in Texas) and D. diaboli, possessed 2n = 50 chromosomes, with a single pair of NOR-bearing chromosomes. Ineach, the chromosomal NOR was located terminally on the short arm of a small-sized acrocentric chromosome. All of the NOR chromosomes appeared to be homologous in trypsin G-banding pattern. Mean genome sizes ranged from 1.94 picograms (pg) of DNA in D. serena from the Nueces River to 2.09 pg of DNA in D. argentosa from Baker's Crossing in the Devils River. Divergence in genome size among nearly all of the samples of Dionda was less than that maximally observed, on average, between individuals within populations of most North American fishes. Collectively, the chromosomal NOR and genome size data suggest that the taxonomic status of Dionda inhabiting Texas and New Mexico may warrant further inves-