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Issue: Vol. 1397 No. 1: 25 Jan. 2007
Type: Articles
Published: 2007-01-25
DOI: 10.11646/zootaxa.1397.1.7
Page range: 55–62
Abstract views: 31
PDF downloaded: 2

Differences in karyotype between two sympatric species of Gymnotus (Gymnotiformes: Gymnotidae) from the eastern amazon of Brazil

Universidade Federal do Pará. Departamento de Genética, Brazil CAPES Masters Scholarship on Genetics and Molecular Biology¸ Brazil
Universidade Federal do Pará. Departamento de Genética, Brazil CNPq Researcher, Brazil
Department of Biology, University of Central Florida, Orlando, FL, 32816-2368
Centro Federal de Educação Tecnológica – CEFET, Brazil
Centro Jovem de Aquarismo – CENJA, Brazil
Universidade Federal do Pará. Departamento de Genética, Brazil CNPq Researcher, Brazil
Gymnotiformes Cytogenetics Gymnotus carapo Gymnotus mamiraua C-Banding Ag-NOR CMA3 and DAPI

Abstract

In this paper we describe the karyotypes of two sympatric species of Gymnotus from Marajó Island, Pará, in the Eastern Amazon basin of Brazil. One of these species, G. mamiraua, has not previously been identified from this area. Karyotype studies demonstrate that G. cf. carapo Linnaeus, has 2n=42 (30M/SM+12ST/A) and G. mamiraua Albert & Crampton, 2n=54 (50M/SM+4ST). The Nucleolar Organizer Region (NOR) was found in the distal region of the short arm of pair 20 in G. cf. carapo and in the interstitial region of pair 1 of G. mamiraua. Both species have centromeric constitutive heterochromatin (CH) in all chromosomes and some in interstitial or distal regions. In both species, 4´6-Diamidino-2- phenylindole (DAPI) staining has shown banding concordant with C-banding, whereas the Chromomycin A3 (CMA3) staining in both species agrees with the NOR location. The new data and review of cytogenetic data in Gymnotus presented here is concordant with a hypothesis that G. carapo is either a complex of populations, or a complex of morphologically similar cryptic species with distinct karyotypes. These taxa may be reproductively isolated by prezygotic reproductive isolation barriers (such as the structure of the Electric Organ Discharge), or by post-zygotic barriers (such as karyotypic formula). The understanding of the cytogenetic structure of G. carapo, combined with associated studies of signal diversity, will yield insight into the mechanisms underlying the origins and maintenance of high species diversity in Gymnotus.

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