A Monophyletic ZW Sex Chromosome System in Leporinus (Anostomidae, Characiformes)

Abstract

Leporinus is a fish group rich in species which occurs from Central America to the River Plate basin in South America. From a cytologic viewpoint, this group is characterized by the occurrence of both homogametic and heterogametic species, a fact that renders it highly interesting for the study of sex chromosome evolution. In the present paper we report new occurrences of ZW sex chromosomes in L. trifasciatus from the Amazon region and L. conirostris from the basin of Eastern Brazil. Considerations about the origin and distribution of these sex chromosomes within the genus are also presented. The material was analyzed by standard Giemsa staining, by silver nitrate staining for the localization of nucleolar organizer regions, and by C banding for heterochromatin identification. The two species presented 2n=54 for both sexes as well as a large subtelocentric chromosome, the largest in the complement, exclusively detected in females, characterizing a W chromosome in both species. The heterochromatin data obtained permit us to assume that this system involves the same chromosomes not only in the species reported here but also in four others reported in previous studies. Thus the ZW system seems to have arisen only once in Leporinus and currently represent a unit of species more related to one another and cytologically distinct from the remaining species in the genus. © 1995, Japan Mendel Society, International Society of Cytology. All rights reserved.