KARYOTYPES OF CUALAC TESSELATUS AND FLORIDICHTHYS CARPIO: COMMENTS ON THE PHYLOGENETIC DISTRIBUTION OF MULTIPLE SEX CHROMOSOMES IN NORTH AMERICAN CYPRINODONTIDS

摘要

Close relatives of the small genera Cualac (one species) and Floridichthys (two species) in the family Cyprinodontidae show sexual differences in chromosome number, with females having 2n = 48 and males having 2n = 47 with a large Y chromosome representing chromosomal fusion. However, karyotypic analysis of both sexes in F. carpio and C. tesselatus revealed the typical cyprinodontid karyotype, with 2n = 48, one normal-sized metacentric to submetacentric chromosome pair, and a graded series of 23 acrocentric or subtelocentric pairs. The phylogenetic pattern suggests that sexually dimorphic karyotypes have arisen independently on two separate occasions in a group that otherwise shows unusually high stability in chromosome morphology.