Karyotype description of five species of Trichomycterus (Teleostei: Siluriformes: Trichomycteridae)

Abstract

Trichomycteridae is a family of small catfish which are widely distributed throughout Southern Central America and South America. The present study showed that the cis-Andean species Trichomycterus florensis, Trichomycterus sp. aff. Trichomycterus itatiyae, Trichomycterus reinhardti, Trichomycterus davisi and Trichomycterus auroguttatus had 2n = 54 chromosomes (42 metacentric, 10 submetacentric and 2 subtelocentric), with T. reinhardti, T. auroguttatus and T. sp. aff. T. itatiyae exhibiting only one chromosome pair with silver-stained nucleolus organizer regions (NORs). The cytogenetic data suggest the existence of at least two groups of species in the cis-Andean representatives of the genus Trichomycterus. In the first group the first metacentric pair is considerably larger than the second metacentric pair and the NORs occur in the pericentromeric position of the short arm of a large submetacentric pair while in the second group the first and second metacentric pairs are about the same size and larger than the other metacentric pairs and the NORs are located in the pericentromeric position of the long arm of a large metacentric pair. The relative conservatism of the karyotype of the cis-Andean Trichomycterus species contrasts with the wide diversification observed in the trans-Andean species, reinforcing the hypothesis that the genus is not monophyletic.

Cytogenetics of <i>Trichomycterus brasiliensis</i> (Siluriformes: Trichomycteridae) from the Upper S&atilde;o Francisco River Basin (MG)

“…Most species of Trichomycteridae family has 2n=54 (Sato et al 2004), very close to the presumed ancestral karyotype of the Order Siluriformes suggested by Oliveira and Gosztonyi (2000), confirming the ancestry of the family. Moreover, among karyotyped species of the family, Trichogenes longipinnis with 2n=54 is considered the most ancestral (Lima and Galetti 1990).…”

“…The diploid number (2n=54) reported in Trichomycterus brasiliensis of the Araras River was observed in virtually all congeners distributed in the cis-Andean region of South America (Sato et al 2004); only T. diabolus, with 2n=56 (Torres et al 2004), presented another diploid number. Chromosomal stability observed in these taxa was not expected due to the biological characteristics of the species of this genus, which are usually highly adapted to specific habitats (Caramaschi 1986).…”

“…In the species of the second group, the first two pairs of metacentric chromosomes are approximately equal in size and pericentromeric NORs are present on the long arms of metacentric chromosomes. The species T. reinhardti (Sato et al 2004), T. auroguttatus (Sato et al 2004) and T. Spegazzini (Gonzo et al 2000) also have the characteristics of the first group, indicating a possible relationship between these taxa and T. brasiliensis.…”

“…Comparing the relative sizes of the first pair of metacentric chromosomes and the location of the NOR, Sato et al (2004) grouped the cis-Andean species of Trichomycterus into two groups. T. brasiliensis belongs to the first group which consists of species that have the first pair of metacentric considerably larger than the second pair and NORs located in a pericentromeric position of the short arm of a large submetacentric chromosome.…”

“…to 2n=64 in Vandellia cirrhosa, although most species of this family have 2n=54 chromosomes (Sato et al 2004). About 20 species of the Trichomycteridae family were studied cytogenetically until now, and represent only a small fraction of the total species of the group.…”