Ploidy levels in silverside fishes, Atherinidae: Menidia on the Texas, U.S.A., coast: Flow-cytometric analysis of the occurrence of allotriploidy.

Flow cytometry of nuclear DNA fluorescence in erythrocytes, coupled with gene dosage assessments derived from electrophoresis of proteins, reaffirmed that the Menidia clarkhubbsi complex of unisexual atherinid fishes is diploid. Non-recombinant hybrids between M. beryllina and M. peninsulae represented 18% (108 specimens) of the Menidia collected from three pools in the Copano Bay area and 9.6% (42 specimens) of those from a pool on Galveston Island. Of those hybrids, 35 and 5%, respectively, were triploids. Zymograms indicated that the triploids either had two doses of genes from M. beryllina and one from M. peninsulae or they had one from the former species and two from the latter. The hybrids seem to be maintained primarily, if not entirely, by ongoing hybridization and back-crossing of F1 hybrids to the parental species. Triploids apparently result from the combination of unreduced, diploid gametes from F1 hybrids with haploid gametes from either M. berylina of M. peninsulae.