title: ZZ/ZW sex chromosome system in the endangered fish Lignobrycon myersi Miranda-Ribeiro, 1956 (Teleostei, Characiformes, Triportheidae).
abstract: Lignobrycon myersi is an endemic fish species from a few coastal rivers in northeastern Brazil. Based on molecular evidence, Lignobrycon myersi and genera Triportheus Cope, 1872, Agoniates Müller & Troschel, 1845, Clupeacharax Pearson, 1924 and Engraulisoma Castro, 1981 were placed in the family Triportheidae. In the present work, we report the first cytogenetic data for Lignobrycon myersi to test the hypothesis that Lignobrycon and Triportheus are closely related. Studied specimens presented 2n=52 with 28 metacentric (m), 18 submetacentric (sm) and six subtelocentric (st) chromosomes for males and 27 m, 19 sm and 6 st for females, characterizing a ZZ/ZW sex chromosome system. The Z chromosome corresponds to the largest chromosome in karyotype while the W is about 50% smaller than the Z and largely heterochromatic. Terminal nucleolus organizer regions, GC-rich sites and 18S rDNA signals were detected on pair 14. However, additional 18S rDNA sites were observed in the W chromosome. The 5S rDNA was mainly detected on long arms of pair 7. The apparent synapomorphic chromosomal traits of Triportheus and Lignobrycon myersi reinforce their close phylogenetic relationship, suggesting that the ZZ/ZW chromosome system in both genera has arisen before cladogenic events.
authors.affiliation: Universidade Estadual do Sudoeste da Bahia (UESB), Dep. Ciências Biológicas, Av. José Moreira Sobrinho, s/n, 45206-190 Jequié, BA, Brazil.
authors.forename: Alexandre Dos Santos
authors.initials: Ados S
authors.lastname: Rodrigues
authors.affiliation: Universidade Estadual de Santa Cruz (UESC), Campus Soane Nazaré de Andrade, Rodovia Jorge Amado, Km 16, 45662-900 Ilhéus, BA, Brazil.
authors.forename: Aline Souza
authors.initials: AS
authors.lastname: Medrado
authors.affiliation: Universidade Estadual do Sudoeste da Bahia (UESB), Dep. Ciências Biológicas, Av. José Moreira Sobrinho, s/n, 45206-190 Jequié, BA, Brazil.
authors.forename: Débora
authors.initials: D
authors.lastname: Diniz
authors.affiliation: Universidade Estadual Paulista, Instituto de Biociências, Dep. Morfologia, 18618-000 Botucatu, SP, Brazil.
authors.forename: Claudio
authors.initials: C
authors.lastname: Oliveira
authors.affiliation: Universidade Estadual do Sudoeste da Bahia (UESB), Dep. Ciências Biológicas, Av. José Moreira Sobrinho, s/n, 45206-190 Jequié, BA, Brazil.
authors.forename: Paulo Roberto Antunes de Mello
authors.initials: PR
authors.lastname: Affonso
keywords: Evolution; Triportheus; female heterogamety; rDNA; sex determination