Karyotypic diversity and chromosome evolution in the armored catfishes Callichthyinae (Siluriformes, Callichthyidae)

Abstract

The Callichthyinae subfamily is composed of five genera with a small number of described species. Molecular cytogenetics studies show the scarcity of records for this subfamily. The aim of the present study was to employ cytogenetic parameters in the analysis of three species belonging to the subfamily Callichthyinae sampled from the Paraná River (Brazil). Callichthys callichthys had 2n = 56 chromosomes (26 m-sm + 30 st-a); Lepthoplosternum pectorale had 2n = 64 chromosomes (8 m-sm + 56 st-a); and Hoplosternum littorale had 2n = 60 chromosomes (8 m-sm + 52 st-a). Regarding the location of the nucleolar organizer regions (NORs) (Ag-staining and 18S rDNA-FISH), different situations were found: single NORs in H. littorale and C. callichthys; multiple NORs in L. pectorale, with intra-individual and inter-individual variation. Heterochromatin was observed in the centromeric region in the chromosomes of the three species. Equilocal, interstitial bands were also found in H. littorale. Physical mapping of 5S ribosomal genes by FISH shows eight 5S rDNA sites in C. callichthys; four 5S rDNA sites in H. littorale and six 5S rDNA sites in L. pectorale. Using cytogenetic markers (diploid number, chromosome formula, NORs, heterochromatin distribution pattern and 5S and 18S rDNA sites), the chromosomal evolution in Callichthyinae is presented: Callichthys shows mostly basal chromosomal conditions, with mostly derived chromosomal conditions verified for the Hoplosternum-Dianema clade and Megalechis-Lepthoplosternum clade. © 2014 © 2014 Dipartimento di Biologia Evoluzionistica, Università di Firenze.