ABSTRACT
Moenkhausia is a highly specious genus among the Characidae, composed of 96 valid species. Only twelve species have a known karyotype. Thus, here are presented the first cytogenetic data of two allopatric populations of Moenkhausia bonita and one of M. forestii, both belonging to the upper Paraná River basin (PR) with discussion on the evolutionary and cytotaxonomic aspects of the genus. The two species presented 2n = 50 chromosomes but different karyotype formulas and occurrence of 1-2 B chromosomes. These elements are small metacentrics in M. bonita and small acrocentrics in M. forestii. In both species, B chromosomes were euchromatic. Ag-NOR sites were found in pair 3 (metacentric), coinciding with fluorescent in situ hybridization (FISH) by the 18S rDNA probe in both species. However, the species differed in terms of the number and position of 5S rDNA sites. Heterochromatic blocks, mapped in M. bonita showed the least amount of heterochromatin in the terminal and pericentromeric regions, while the M. forestii karyotype revealed a greater amount of interstitial heterochromatic blocks. The karyotype distinctions between the two species, including the morphology of B chromosomes, may contribute as a reference in the taxonomic studies in this group.(AU)
Moenkhausia é um gênero altamente especioso dentre os Characidae, composto por 96 espécies válidas, mas apenas doze espécies têm seus cariótipos conhecidos. Portanto, são apresentados aqui os primeiros dados citogenéticos de duas populações alopátricas de Moenkhausia bonita e uma de M. forestii, ambas pertencentes à bacia do alto rio Paraná (PR), com uma ampla discussão sobre os aspectos evolutivos e citotaxonômicos do gênero. As duas espécies apresentaram 2n = 50 cromossomos, mas diferentes fórmulas cariotípicas e ocorrência de 1-2 cromossomos B. Esses elementos são pequenos metacêntricos em M. bonita e acrocêntricos pequenos em M. forestii. Em ambas as espécies, os cromossomos B apresentaram-se eucromáticos. Sítios Ag-NOR foram encontrados no par 3 (metacêntrico), coincidindo com a hibridização fluorescente in situ (FISH) pela sonda 18S rDNA em ambas as espécies. No entanto, as espécies diferiram em termos de número e posição dos sítios de 5S rDNA. Blocos heterocromáticos mapeados em M. bonita revelaram pequena quantidade de heterocromatina nas regiões terminal e pericentromérica, enquanto o cariótipo de M. forestii revelou uma maior quantidade de blocos heterocromáticos intersticiais. As distinções cariotípicas entre as duas espécies, incluindo a morfologia dos cromossomos B, podem contribuir como uma referência em estudos taxonômicos neste grupo.(AU)
Subject(s)
Animals , Heterochromatin , Chromosomes , Cytogenetics , Characidae , In Situ Hybridization, FluorescenceABSTRACT
Only one species of armored catfish, Ancistrus cirrhosus Valenciennes 1836, has been historically described in the basin of the Paraná River, from Misiones (Argentina). However, the ample variation found in the morphology and coloration of the populations sampled in the tributaries of the Brazilian state of Paraná makes it difficult to establish the real taxonomic status and evolutionary history of the Ancistrus specimens, suggesting that A. cirrhosus is not the only species found in this basin. By combining data on mitochondrial DNA (COI gene) and chromosomal markers from different Ancistrus populations, totaling 144 specimens, in the tributaries of the Paraná, and specimens from Misiones (type-locality of A. cirrhosus), we detected five distinct evolutionary lineages. All the specimens were 2n = 50, but had four distinct karyotype formulae. The results of the Generalized Mixed Yule Coalescent (GYMC) and the genetic distances (uncorrected P-values) between lineages ranged from 3 to 5%. Clusters of 18S rDNA were observed in a single chromosome pair in seven populations of Ancistrus, but at different positions, in some cases, in synteny with the 5S rDNA sites. Multiple 5S sites were observed in all populations. Overall, the cytogenetic data reinforce the genetic evidence of the diversification of lineages, and indicate the existence of candidate species in the study region. The evidence indicates that at least four candidate species of the Ancistrus may coexist in the Paraná basin besides A. cirrhosus. Overall, our results provide a comprehensive scenario for the genetic variation among Ancistrus populations and reinforce the conclusion that the true diversity of the freshwater fish of the Neotropical regions has been underestimated.