Citótipo Exclusivo para Parauchenipterus galeatus (Siluriformes, Auchenipteridae) na Bacia do Atlântico NE Oriental do Brasil: Indicações de um Complexo de Espécies

Abstract

RESUMO. Endemismos entre as ictiofaunas das bacias hidrográficas brasileiras vêm se mostrando frequentes, principalmente decorrentes de vicariância ou dispersão. Diversas espécies constituem verdadeiramente complexos de espécies crípticas, em franco processo de diferenciação. Análises citogenéticas realizadas no bagre, Parauchenipterus galeatus, da bacia hidrográfica do NE Oriental do Brasil revelaram um cariótipo com 2n=58 (24m+16sm+10st+8a; NF=108), com RONs simples localizadas em região distal de um par cromossômico submetacêntrico, com regiões heterocromáticas reduzidas. Este padrão cariotípico se mostra diferenciado de outros já descritos para a espécie de outras bacias hidrográficas. A distribuição da heterocromatina, associada às variações estruturais do cariótipo representam importantes indícios de diferenciação citogenética de P. galeatus em diferentes bacias brasileiras. Considerando o tempo de divergência entre as grandes bacias, é possível que as diferenças citogenéticas encontradas possam representar em alguns casos efetivas barreiras reprodutivas pószigóticas. A diversidade cariotípica para a espécie apoia a existência de um complexo de espécies. Palavras-chave: cangati, espécies crípticas, citogenética de peixes, especiação alopátrica. ABSTRACT: Exclusive cytotype in Parauchenipterus galeatus (Siluriformes, Auchenipteridae) in the Eastern Northeast Atlantic basin of Brazil: indication of a species complex. Endemisms among the ichthyofauna of the hydrographic Brazilian basins has been showed frequent, mainly due to vicariance or dispersal processes. Several species constitute genuinely complexes of cryptic species, in clear process of differentiation. Cytogenetic analysis performed in the catfish, Parauchenipterus galeatus, in the basin of the Eastern Northeast Atlantic basin of Brazil revealed a karyotype with 2n = 58 (24m+16sm+10st+8a; NF=108), with unique NORs sites located in the distal region of a submetacentric chromosome pair and with reduced heterochromatic regions. This standard karyotype shown differentiated from other already described for species of others basins. The distribution of heterochromatin associated with structural variations of karyotype represent important evidences of cytogenetic differentiation of P. galeatus among the different Brazilian basins. Considering the time of divergence between large basins, it is possible that the cytogenetic differences found may represent in some cases effective post-zygotic reproductive barriers. The diversity of the species karyotype supports the existence of a species complex.

Possible Common Origin of B Chromosomes in Neotropical Fish (Siluriformes, Auchenipteridae) Reinforced by Repetitive DNA Mapping

“…The data obtained in the present study show that B chromosomes organization in the two species is little different from A chromosomes organization, besides indicating a great similarity in the B chromosomes composition of these two species. It is important to note that the population of P. galeatus from Lagoa da Prata [13, present work] is the only one that presented B chromosomes, which represents 20% of all analyzed populations of this species, considering only published data [13,18,20,36]. These similarities suggest common origin for these chromosomes of P. galeatus and Trachelyopterus sp.…”

“…in this paper reinforce this proximity, since they evidenced high chromosome similarities: maintenance of the diploid number (2n=58), heterochromatin dispersed in the terminal region of the most of A chromosomes, single terminal NORs located in the short arm of a subtelocentric pair (confirmed by FISH with 18S rDNA), two pairs bearing 5S rDNA sites, and similarities between B chromosomes. The few number of Auchenipteridae studies [13,[18][19][20][21][22][23][24]36] suggest that this conserved chromosome macrostructure is recurrent in the family, and most of the differences found are usually due to non-robertsonian rearrangements [18]. This situation of little variation is not unique to these species, since many groups of Neotropical fish exhibit relative karyotype conservatism [37][38][39].…”

“…In all Auchenipteridae species analyzed by the cytogenetics, the NORs are simple, but their location may be interstitial or terminal, according to species. In A. inermis [19], P. galeatus [13,18,20,36], T. jaracatia, T. neivai [22], A. inermis [23], and Trachelyopterus sp. (this paper) NORs were terminal; in A. osteomystax [20], G. ribeiroi [20,21,24], and T. atronasus [19] NORs were interstitial.…”