%0 Journal Article
%T Abstract
%A Sandra Mariotto
%A Liano Centofante
%A Orlando Moreira-Filho
%J Neotropical Ichthyology
%D 2013
%I Sociedade Brasileira de Ictiologia
%X Cytogenetic analyses were carried out in 117 specimens of seven species of the genus Ancistrus from three hydrographic in Mato Grosso State: Paraguay, Araguaia-Tocantins and Amazon basins. Conventional cytogenetic techniques were used to obtain mitotic chromosomes. C-banding was performed to detect heterochromatic regions and silver nitrate staining was used to identify nucleolar organizer regions (Ag-NORs). The counted and paired chromosomes revealed diploid numbers ranging from 2n = 40 to 2n = 54 with karyotype formulae varying from FN = 80 to FN = 86. Single marks in distinct chromosomes identified the nucleolar organizer regions. The constitutive heterochromatin was scarce in the diploid number from 2n = 50 to 2n = 54 and conspicuous blocks were observed in a single species with 2n = 40 chromosomes. These data corroborate the hypotheses of reduction of diploid number in species with derived features such as presence of sex chromosomes and polymorphisms, besides allowing inferences about the evolutionary mechanisms and the ancestor karyotype that favored the diversification of this important genus in the tribe Ancistrini. Foram realizadas an¨¢lises citogen¨¦ticas de 117 esp¨¦cimes do g¨ºnero Ancistrus de tr¨ºs bacias hidrogr¨¢ficas do estado de Mato Grosso: Paraguai, Araguaia-Tocantins e Amaz nica, utilizando as t¨¦cnicas de citogen¨¦tica convencional para obten  o de cromossomos mit¨®ticos, visualiza  o de regi es heterocrom¨¢ticas e regi es organizadoras de nucl¨¦olos. Os cromossomos pareados revelaram uma varia  o no n¨²mero diploide de 2n = 40 a 2n = 54 e n¨²mero fundamental de NF = 80 a NF = 86. As regi es organizadoras de nucl¨¦olos foram evidenciadas em um ¨²nico par de cromossomos para todas as esp¨¦cies e a heterocromatina ¨¦ escassa nas esp¨¦cies com n¨²meros diploides elevados (2n = 50 a 2n = 54). Os blocos heterocrom¨¢ticos mais evidentes foram observados nos pares portadores das AgRONs e em cromossomos da esp¨¦cie com 2n = 40. Estes dados contribuem para a hip¨®tese de redu  o do n¨²mero diploide nas esp¨¦cies que apresentam polimorfismos cromoss micos e cromossomos sexuais, al¨¦m de contribuir para infer¨ºncias sobre os mecanismos de evolu  o cariot¨ªpica que favoreceu a diversifica  o do g¨ºnero Ancistrus, o mais representativo na tribo Ancistrini.
%K AgNOR
%K Cytogenetic
%K Diploid number
%K Heterochromatin
%U http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-62252013000100125