No abstract

Some species of the genus Characidium have heteromorphic ZZ/ZW sex chromosomes with a totally heterochromatic W chromosome. Methods for chromosome microdissection associated with chromosome painting have become important tools for cytogenetic studies in Neotropical fish. In Characidium cf. fasciatum, the Z chromosome contains a pericentromeric heterochromatin block, whereas the W chromosome is completely heterochromatic. Therefore, a probe was produced from the W chromosome through microdissection and degenerate oligonucleotide-primed polymerase chain reaction amplification. FISH was performed using the W probe on the chromosomes of specimens of this species. This revealed expressive marks in the pericentromeric region of the Z chromosome as well as a completely painted W chromosome. When applying the same probe on chromosome preparations of C. cf. gomesi and Characidium sp., a pattern similar to C. cf. fasciatum was found, while C. cf. zebra, C. cf. lagosantense and Crenuchus spilurus species showed no hybridization signals. Structural changes in the chromosomes of an ancestral sexual system in the group that includes the species C. cf. gomesi, C. cf. fasciatum and Characidium sp., could have contributed to the process of speciation and could represent a causal mechanism of chromosomal diversification in this group. The heterochromatinization process possibly began in homomorphic and homologous chromosomes of an ancestral form, and this process could have given rise to the current patterns found in the species with sex chromosome heteromorphism.

Cytogenetic analysis of Potamotrygon aff. motoro and P. falkneri indicated the occurrence of an X1X1X2X2/X1X2 Y multiple sex chromosome system in both species, with 2n = 66 chromosomes for females and 2n = 65 chromosomes for males. The nucleolus organizer regions (NORs) identified using Ag-NOR technique showed that both species have multiple Ag-NORs (5 to 7 chromosomes stained). C-banding technique indicated the presence of heterochromatic blocks in the centromeric regions of almost all chromosomes in both species. Through this study there was evidence of heterogeneity in the karyotypes, which suggests that chromosomal rearrangements such as inversions and/or translocations occurred during the chromosomal evolution in two species of this genus.
Análises citogenéticas de Potamotrygon aff. motoro e P. falkneri identificaram a ocorrência de um sistema múltiplo de cromossomos sexuais do tipo X1X1X2X2/X1X2Y, em ambas as espécies, com 2n = 66 cromossomos em fêmeas e 2n = 65 cromossomos nos machos. As regiões organizadoras de nucléolos (RONs) identificadas pela reação Ag-RON, evidenciaram marcações múltiplas em ambas as espécies (com variações de 5 a 7 RONs). A técnica de bandamento C, revelou a presença de blocos heterocromáticos localizados nas regiões centromérica em quase todos os cromossomos nas duas espécies em estudo. Através do presente estudo foi evidenciada uma heterogeneidade nos cariótipos, permitindo sugerir que rearranjos cromossômicos, como inversões e/ou translocações, ocorreram durante a evolução cromossômica nas duas espécies desse gênero

In the present study, five callichthyid species belonging to the subfamily Corydoradinae were karyotyped: three species of Aspidoras and two of Corydoras. The three species of Aspidoras had the same diploid number, 2n = 46 chromosomes, similar karyotypic formulae, with most chromosomes metacentric or submetacentric, single interstitial Ag-NORs and C-band positive segments mainly found in the centromeric position. The comparative analysis of cytogenetic data available for the genus Aspidoras and other species of Corydoradinae suggest that several events of centric fusion occurred in the origin of the species of Aspidoras. The two analyzed species of Corydoras showed high diploid numbers, 2n = 74 in C. sodalis and 2n = 90 in C. britskii. While C. sodalis exhibited single Ag-NORs and terminal, interstitial and centromeric C-band positive segments in almost all chromosomes, C. britskii showed multiple Ag-NORs and a small number of C-band positive segments found in the terminal position in one acrocentric (A) pair and in the interstitial position in one subtelocentric (ST) pair. The occurrence of high diploid numbers and many ST and A chromosomes are uncommon among the Corydoradinae, suggesting the occurrence of a high number of chromosome rearrangements, mainly centric fissions, in the origin of the Corydoras species studied.

The combination of cytogenetic and molecular data with those traditionally obtained in areas like systematics and taxonomy created interesting perspectives for the analysis of natural populations under different aspects. In this context, this study aimed to evaluate the genetic differentiation among populations of the genus Hemiodontichthys Bleeker, 1862, through combined genetic techniques and included the analysis of populations sampled in the Araguaia River, Guamá River, Madeira River and two populations from the Purus River. Hemiodontichthys samples from the two localities in Purus River were also karyotyped in order to address the degree of chromosomal variation between populations. Through GMYC analysis of the COI tree, the patterns of genetic variation among local populations revealed to be higher than the ones found among distinct species from other genera of the subfamily Loricariinae, suggesting the existence of probable four cryptic species in this genus. The possible existence of a species complex in the genus is corroborated by the different cytogenetic patterns between Hemiodontichthys sp. 1 and sp. 2, revealing the necessity of a deep taxonomic review of the group.

The Pantanal is under the influence of the Paraguay River flood regime is considered to be one of the largest wetlands of the world, and has rich biodiversity, including fishes. Until now, the identification of fish species in this biome has only considered the morphological characteristics of individuals, and the present work aimed to identify the fish species of the Pantanal region through the DNA barcode methodology for investigating the biodiversity in this region. The genetic analysis of 638 samples via the GMYC approach identified 137 operational taxonomic units (OTUs) belonging to 127 species that have previously been described according to their morphological characteristics. Data suggest that 10 cases of morphospecies (Eigenmannia trileneata, E. virescens, Pimelodella gracilis, Brachyhypopomus pinnicaudatus, Brachyhypopomus sp., Ancistrus sp., Hyphessobrycon eques, Jupiaba acanthogaster, and Serrapinnus calliurus) represent complexes of cryptic species, and the number of species described in the Pantanal region has thus potentially been underestimated.