Diploidy and triploidy in the hybrid minnow,Phoxinus eos x Phoxinus neogaeus (Pisces: Cyprinidae)

Summary Two presumptive hybrid populations are examined. Nebraskan hybrids, all having allozymic F1 electromorphs, exist as both diploid (2n=50) and triploid (3n=75) forms. This supports the hypothesis of parthenogenesis as the mode of hybrid reproduction. The maximum number of nucleoli per cell is suggested as an indicator of ploidy level. In contrast, electrophoretic analysis of a postulated Mendelian hybrid population in Quebec failed to detect any allozymic heterozygotes or recombinants. A previous conclusion of introgressive hybridization in this population is not supported.This research was supported by the Theodore Roosevelt Memorial Fund. We wish to thank Arthur Ostrowski for his generous assistance. Collection of the Quebec specimens was made possible through the kindness of Etienne Magnin. We acknowledge the Department of Biological Sciences, Wayne State University, for providing research facilities.