Chromosomal Diversity in Two Allopatric Populations of Farlowella hahni Meinken 1937 (Teleostei: Siluriformes): Cytogenetics and Cytochrome b Analyses.

Farlowella is the second richest genus in Loricariinae, broadly distributed in freshwater streams and rivers of South America. In this article, we aimed to expand on the cytogenetic and molecular data available for two allopatric populations of Farlowella hahni. Both populations had diploid chromosome number 58, but with karyotype differences, indicative of chromosomal rearrangements. C-banding showed large heterochromatic blocks at telomeric regions in acrocentric chromosomes in both populations. Fluorescence in situ hybridization (FISH) revealed a single 18S rDNA site in both populations and a single 5S rDNA site for individuals from lower Paraná River basin (native region) and multiple 5S rDNA sites for individuals from upper Paraná River basin (non-native region). Mitochondrial sequence analyses did not separate the two F. hahni populations. The cytogenetic and molecular data obtained are relevant in a preliminary study and suggested the existence of cryptic diversity and the hypothesis that at least two Farlowella lineages may coexist in the Paraná basin.

Cytogenetic markers as tools in delimiting species of the highly diverse Neotropical fish Bryconamericus (Characiformes: Characidae)

Bryconamericus is a highly diverse group of characid fishes, being cytogenetic a valuable tool for the delimitation of species. Bryconamericus aff. iheringii (Upper Uruguay/Lower Paraná), B. coeruleus (Upper Paraná), B. cf. ecai e B. cf. eigenmanni (Upper Uruguay) were studied cytogenetically, and presented 2n=52 chromosomes, with interpopulational/interspecific variation of karyotype and fundamental number. Heterochromatin was evidenced in pericentromeric, telomeric and interstitial regions, and it was shown to be an important cytogenetic marker. Single nucleolar organizing regions (NORs) were found in B. cf. eigenmanni, B. cf. ecai and B. aff. iheringii (Lower Paraná), and multiple in B. aff. iheringii (Upper Uruguay) and B. coeruleus, with occurrence of two patterns for the first species, and three for the second. The 5S/18S rDNA-FISH confirmed the location of the NORs and showed single 5S rDNA cistrons only in B. aff. iheringii (Lower Paraná), evidencing the dispersion of both genes, often co-located, in the karyotype of the others species. The data of this work contribute for the delimitation of the species of the genus. Co-localization of ribosomal genes may represent a plesiomorphic condition for the group, and their dispersion suggest the occurrence of duplication, pseudogeneization and transposition events mediated by mobile genetic elements.(AU)

Bryconamericus é um grupo altamente diverso de caracídeos, sendo a citogenética uma valiosa ferramenta para a delimitação de espécies. Bryconamericus aff. iheringii (Alto Uruguai/Baixo Paraná), B. coeruleus (Alto Paraná), B. cf. ecai e B. cf. eigenmanni (Alto Uruguai) foram estudados citogeneticamente, e apresentaram 2n=52 cromossomos, com variação interpopulacional/interespecífica de cariótipo e número fundamental (NF). Heterocromatinas foram evidenciadas nas regiões pericentromérica, telomérica e intersticial, e mostrou-se um importante marcador citogenético. Regiões organizadores de nuclcéolos (RONs) simples foram encontradas em B. cf. eigenmanni, B. cf. ecai e B. aff. iheringii (Baixo Paraná), e múltiplas em B. aff. iheringii (Alto Uruguai) e em B. coeruleus, com a ocorrência de dois padrões de localização para a primeira espécie, e três para a segunda. A FISH-DNAr 5S/18S confirmou a localização das RONs e mostrou cístrons simples de DNAr 5S apenas em B. aff. iheringii (Baixo Paraná), evidenciando a dispersão de ambos os genes, muitas vezes co-localizados, no cariótipo das demais espécies. Os dados deste trabalho contribuem para a delimitação das espécies do gênero. A co-localização dos genes ribossomais pode representar uma condição plesiomórfica para o grupo, e sua dispersão sugere a ocorrência de eventos de duplicação, pseudogenização e transposição mediada por elementos genéticos móveis.(AU)

Morphologically Cryptic Species of the Astyanax bimaculatus "Caudal Peduncle Spot" Subgroup Diagnosed Through Cytogenetic Characters.

Astyanax is a species-rich polyphyletic genus distributed between the southern United States and central Argentina. The genus contains groups of cryptic species, which are difficult to distinguish, and are sometimes identified wrongly. Basic and molecular cytogenetic analyses were run on Astyanax abramis and three junior synonyms of Astyanax lacustris: Astyanax altiparanae, from the upper Paraná River basin, Astyanax asuncionensis, from the lower Paraná basin, and Astyanax jacuhiensis, from the upper Uruguay River. These species all belong to the Astyanax bimaculatus group. All species presented 2n = 50 chromosomes and single nucleolar organizing regions (NORs). In A. altiparanae, the karyotype was 6m + 28sm+4st+12a and the NORs were present in pair 20, while A. jacuhiensis was 8m + 28sm+6st+8a, with NORs in pair 22, and A. asuncionensis was 8m + 24sm+6st+12a, with NORs in pair 20. A. abramis was 4m + 30sm+8st+8a with NORs in pair 22. Fluorescence in situ hybridization revealed single 5S rDNA cistrons in A. altiparanae and A. asuncionensis, and multiple (4) cistrons in A. abramis and A. jacuhiensis. Heterochromatin had a distinct distribution in each species, but was predominantly centromeric and interstitial proximal. In A. abramis and A. asuncionensis, the first acrocentric chromosome pair presented centromeric, telomeric, and interstitial-proximal heterochromatin in the long arm, which may represent the presence of homologous chromosomes in these species. While there are some cytogenetic similarities, differences in the location of 5S rDNA, distribution of heterochromatin, and karyotype formulae contribute to the differentiation of the study species, and support the identification of phylogenetically proximate groups in the "Astyanax clade."