Cytogenetics of Gymnogeophagus setequedas (Cichlidae: Geophaginae), with comments on its geographical distribution

Abstract

We provide cytogenetic data for the threatened species Gymnogeophagus setequedas, and the first record of that species collected in the Iguaçu River, within the Iguaçu National Park's area of environmental preservation, which is an unexpected occurrence for that species. We verified a diploid number of 2n = 48 chromosomes (4sm + 24st + 20a) and the presence of heterochromatin in centromeric and pericentromeric regions, which are conserved characters in the Geophagini. The multiple nucleolar organizer regions observed in G. setequedas are considered to be apomorphic characters in the Geophagini, whereas the simple 5S rDNA cistrons located interstitially on the long arm of subtelocentric chromosomes represent a plesiomorphic character. Because G. setequedas is a threatened species that occurs in lotic waters, we recommend the maintenance of undammed environments within its known area of distribution.Keywords: Chromosomes, Conservation, Iguaçu River, Karyotype, Paraná River.Fornecemos dados citogenéticos para a espécie ameaçada Gymnogeophagus setequedas, e o primeiro registro da espécie coletado no rio Iguaçu, na área de preservação ambiental do Parque Nacional do Iguaçu, a qual é uma área de ocorrência inesperada para esta espécie. Verificamos em G. setequedas 2n = 48 cromossomos (4sm + 24st + 20a) e heterocromatina presente nas regiões centroméricas e pericentroméricas, as quais indicam caracteres conservados em Geophagini. Múltiplas regiões organizadoras de nucléolos foram observadas em G. setequedas e são consideradas características apomórficas em Geophagini, enquanto cístrons de DNAr 5S simples e localizados intersticialmente no braço longo de cromossomos subtelocêntricos representam uma característica plesiomórfica. Visto que G. setequedas é uma espécie ameaçada de extinção que ocorre em águas lóticas, recomendamos a manutenção de ambientes livre de barragens em sua área de distribuição.

Genetic Diversity of the Endangered Neotropical Cichlid Fish (Gymnogeophagus setequedas) in Brazil

“…However, it seems that this species behaves differently from its congeners, preferring fast waters. This fact was corroborated by its recent capture in the Lower Iguaçu River, in stretches without containment and with fast waters ( Paiz et al, 2017 ). In addition, this species disappeared after construction of the Itaipu reservoir, being collected only twice, suggesting its dependence on lotic environments ( Agostinho et al, 2004 ).…”

“…However, since its description no specimens have been collected in the original known distribution area ( Abilhoa and Duboc, 2004 ; Agostinho et al, 2004 ; Pavanelli and Reis, 2008 ). Nevertheless, 15 specimens of G. setequedas were recently collected in the Lower Iguaçu River, both up and downstream from Iguaçu Falls in the Iguaçu National Park ( Paiz et al, 2017 ). According to the authors, finding this species in that region was quite unexpected as the Iguaçu waterfalls have lead to effective geographic isolation of the Ichthyofauna of the Iguaçu River ( Zawadzki et al, 1999 ), providing an accentuated degree of endemicity, estimated between 51 and 71% ( Abell et al, 2008 ).…”

Chromosome comparison among five species of Neotropical cichlids of Cichlasoma and Gymnogeophagus (Perciformes)

“…In the Geophagini and Cichlasomatini tribes, as in Cichlidae in general, the pattern of single NORs is the most common one (Poletto et al, 2010), indicating that this characteristic can be considered plesiomorphic. Reports of multiple NORs, confirmed by FISH in cichlids, are scarce, and were reported in only seven species, including those described in this study: Mesonauta festivus (Poletto et al, 2010), Symphysodon aequifasciatus S. discus and S. haraldi (Gross et al, 2010), and Gymnogeophagus setequedas (Paiz et al, 2017). It is worthy of note that four of these species of the genera Mesonauta and Symphysodon belong to the Heroini tribe, considered as derived within the subfamily Cichlinae.…”

“…Gymnogeophagus rhabdotus presented two chromosomal pairs bearing ribosomal cistrons, an unusual pattern in the Geophaginae tribe, even though only few species were analyzed. However, there are reports of single NORs in Geophagus brasiliensis, Gymnogeophagus gymnogenys, and Satanoperca acuticeps (Brum et al, 1998;Feldberg et al, 2003;Pires et al, 2010), and multiple NORs only in Gymnogeophagus setequedas (Paiz et al, 2017). In population B of C. paranaense, a chromosomal pair and two non-homologous chromosomes (chromosomes 5 and 11) with ribosomal cistrons were observed; chromosome 5 had an interstitial signal, coincident with the heterochromatin, but not corresponding to AgNOR sites.…”

“…Most of the species of Neotropical cichlids, approximately 60%, present a karyotype with 2n = 48, but a variation from 2n = 32 to 2n = 60 is observed, and chromosomal rearrangements have already been reported in the family (Feldberg et al, 2003;Poletto et al, 2010). Several cytogenetic analyses with the Cichlasomatini tribe show great chromosomal variation in this tribe (Feldberg et al, 2003) in contrast with low ecomorphological diversity, compared with other tribes, such as Geophagini (López-Fernandes et al, 2013), with few chromosomal data (Feldberg and Bertollo, 1984;Pires et al, 2010;Paiz et al, 2017). Hence, these tribes are of interest for cytogenetic studies.…”