Cytotaxonomic diagnosis of Trichomycterus diabolus (Teleostei: Trichomycteridae) with comments about its evolutionary relationships with co-generic species

Abstract

The karyotype and the Ag-NOR location of a sample of Trichomycterus diabolus collected in the córrego Hortelã (Botucatu, São Paulo, Brazil) are described. The species exhibited 2n=56 chromosomes (42 metacentrics, 12 submetacentrics and 2 subtelocentrics) and the nucleolus organizing region located near to the centromere on the long arm of the largest metacentric pair. The presence of 2n=56 chromosomes in T. diabolus is an interesting characteristic since until now all cis-Andean species karyotyped presented 2n=54 chromosomes while almost all trans-Andean species presented different diploid numbers. The possible origin of this unexpected karyotypic form is discussed.São descritos o cariótipo e a localização das regiões organizadoras de nucléolo (Ag-NOR) de uma amostra de Trichomycterus diabolus, coletada no córrego Hortelã (Botucatu, São Paulo, Brasil). A espécie apresentou 2n=56 cromossomos (42 metacêntricos, 12 submetacêntricos e 2 subtelocêntricos) e as regiões organizadoras de nucléolo localizadas próximas ao centrômero, no braço longo do maior par metacêntrico. A ocorrência de 2n=56 cromossomos em Trichomycterus diabolus é uma característica interessante, uma vez que, até o momento, todas as espécies cis-Andinas cariotipadas apresentaram 2n=54 cromossomos, enquanto que quase todas as espécies trans-Andinas apresentaram números diplóides diferentes. É discutida a possível origem desta inesperada estrutura cariotípica.

Chromosomes, RAPDs and evolutionary trends of the Neotropical fish Mimagoniates microlepis (Teleostei: Characidae: Glandulocaudinae) from coastal and continental regions of the Atlantic forest, Southern Brazil

“…Variable karyotypes associated with vicariant processes and putative speciation have been described for other Neotropical fish groups (Torres et al . 1998, 2004a; Jorge and Moreira‐Filho 2000; Centofante et al . 2003; Bertollo et al .…”

The remarkable species complex Mimagoniates microlepis (Characiformes: Glandulocaudinae) from the Southern Atlantic Rain forest (Brazil) as revealed by molecular systematic and population genetic analyses

“…Contrarily, striking differences in the chromosome formula as well as the number and location of ribosomal cistrons have been documented by comparing samples from the southern and southeastern coastal plains with those native to Iguaçu headwaters (Guimarães et al, 1995;Torres et al, 2008). It is presumed that variations in the number and location of ribosomal cistrons (nucleolar organizer regions-NORs) are diagnostic markers for species level (Galetti et al, 1984;Amemyia & Gold, 1988;Venere & Galetti, 1989;Torres et al, 1998Torres et al, , 2004a.…”

Microstructural chromosome reorganization in the genus Trichomycterus (Siluriformes: Trichomycteridae)

“…However, comparing our results with available cytogenetic data for this group, one must note that remarkable differences in the karyotypic formulae are evident, mainly related to the number of meta-and submetacentric chromosomes in each species or even within a single species (Torres et al, 2004;Vicari et al, 2010).…”

“…to 2n=62 in T. laucaensis (Arratia & Veloso, 1980). Remarkably, Sato et al (2004) stated that such notable differences might be found only in transAndean species, while cis-Andean species have retained a conserved diploid number of 54 chromosomes, except T. diabolus from Tietê River, which has been described with 2n=56 chromosomes (Torres et al, 2004). In addition, variations in the chromosomal location of the nucleolar organizer regions (NORs) and even the occurrence of supernumerary chromosomes were already reported in this group (Borin & Martins-Santos, 2000;Torres et al, 2002).…”