Identification of distinct evolutionary units in allopatric populations of Hypostomus cf. wuchereri Günther, 1864 (Siluriformes: Loricariidae): karyotypic evidence

Abstract

Few chromosomal reports are available for the endemic fish fauna from coastal basins in northeastern Brazil, and regional biodiversity remains partially or completely unknown. This is particularly true for Loricariidae, the most diverse family of armored catfishes. In the present work, allopatric populations of Hypostomus cf. wuchereri (Siluriformes: Loricariidae) from two basins in Bahia (northeastern Brazil) were cytogenetically analyzed. Both populations shared 2n = 76 chromosomes, a karyotype formula of 10m+18sm+48st/a (FN = 104) and single terminal GC-rich NORs on the second metacentric pair. Nevertheless, microstructural differences were detected by C-banding, fluorochrome staining and chromosomal digestion with restriction enzymes (Alu I, Bam HI, Hae III, and Dde I). The population from Una River (Recôncavo Sul basin) showed conspicuous heterochromatin blocks and a remarkable heterogeneity of base composition (presence of interspersed AT/GC-rich and exclusively AT- or GC-rich sites), while the population from Mutum river (Contas River basin) presented interstitial AT-rich C-bands and terminal GC/AT-rich heterochromatin. Each enzyme yielded a specific band profile per population which allowed us characterizing up to five heterochromatin families in each population. Based on the present data, we infer that these populations have been evolving independently, as favored by their geographic isolation, probably representing cryptic species.<br>Poucos dados cromossômicos estão disponíveis para a fauna de peixes endêmicos das bacias costeiras do nordeste do Brasil, e a biodiversidade regional continua a ser parcial ou completamente desconhecida. Isto é particularmente verdadeiro para Loricariidae, a mais diversa família de cascudos. No presente trabalho, populações alopátricas de Hypostomus cf. wuchereri (Siluriformes: Loricariidae) de duas bacias hidrográficas da Bahia (nordeste do Brasil) foram citogeneticamente analisadas. Ambas as populações compartilham 2n = 76 cromossomos, uma fórmula cariotípica de 10m+18sm+48st/a (FN = 104) e um único sinal terminal de RONs GC-ricas no segundo par metacêntrico. No entanto, diferenças microestruturais foram detectados pelo bandeamento C, coloração com fluorocromos e digestão cromossômica com enzimas de restrição (Alu I, BamH I, Hae III e Dde I). A população do rio Una (bacia do Recôncavo Sul) apresentou blocos de heterocromatina conspícuos e grande heterogeneidade de composição de base (presença de sítios AT/GC-ricos intercalados e exclusivamente AT ou GC-ricos), enquanto a população do rio Mutum (bacia do Rio de Contas) apresentou bandas C intersticiais AT-ricas e heterocromatina terminal GC/AT-ricas. Cada enzima gerou um perfil específico de bandas por população que nos permitiu caracterizar até cinco famílias de heterocromatina em cada população. Baseado nos presentes dados, podemos inferir que essas populações têm evoluido de forma independente, favorecidas pelo seu isolamento geográfico, provavelmente representando espécies crípticas

Comparative Cytogenetics Among Three Sympatric Hypostomus Species (Siluriformes: Loricariidae): An Evolutionary Analysis in a High Endemic Region

“…The size heteromorphism of the heterochromatin block in pair 20 of the H. myersi is due to in cis accumulation of repeat sequences 46 . Interstitial bands have also been observed in Hypostomus regani (Ihering, 1905) 18,41 , Hypostomus topavae (Godoy, 1969) 13 , Hypostomus unae (Steindachner, 1878) 43 and Hypostomus wuchereri (Günther, 1864) 42 . The pattern of heterochromatin bands at interstitial positions, which are equidistant in relation to the centromere and equilocal in non-homolog chromosomes of the same diploid group, may occur due to chromosome organization in nucleic interphase that would facilitate the transposition these segments [55][56] .…”

“…Several cytogenetic studies in Hypostomus revealed a great complexity and diversity of information [10][11][12][13][14][15][16][17][18][40][41][42][43][44][45][46] , showing extensive karyotype variation in this group. Cytogenetic analysis evidenced 2n = 54 chromosomes as an ancestral characteristic in Loricariidae, since it was reported in the basal genera and in the sister group Trichomycteridae 47 .…”

“…Cytogenetic analysis evidenced 2n = 54 chromosomes as an ancestral characteristic in Loricariidae, since it was reported in the basal genera and in the sister group Trichomycteridae 47 . Karyotype analyses in Hypostomus have allowed well-defined evolutionary trends, as the occurrence of high variation in the 2n, due to chromosomal rearrangements, like centric fissions [12][13][14][15][16][17][18][19][20][40][41][42][43][44][45][46] , which could explain the increased 2n present in the H. commersoni (2n = 68 chromosomes), H. derbyi (2n = 68 chromosomes) and H. myersi (2n = 74 chromosomes). Chromosome variability in Hypostomus may be assessed by intraspecific variation of 2n, karyotype formula, heterochromatin localization, and number and localization of NORs sites 15,17,44 .…”

A new dark-dotted species of Hypostomus Lacépède (Siluriformes: Loricariidae) from rio Paraguaçu, Bahia State, Brazil

“…Hypostomus jaguar represents the tenth siluriform species that is apparently endemic to the Paraguaçu basin. Weber (2003) mentioned the possibility that H. wuchereri, a species with the vague type locality "Bahia", occurred in the rio Paraguaçu, as previously cited by Bitencourt et al (2011). However, the examination of some of the type material of H. wuchereri revealed that it is a distinct species from H. chrysostiktos and H. jaguar, the two species that are known to occur in the rio Paraguaçu basin.…”

Allopatric chromosomal variation in Nematocharax venustus Weitzman, Menezes & Britski, 1986 (Actinopterygii: Characiformes) based on mapping of repetitive sequences

“…Moreover, the availability of refined cytogenetic methods have allowed identifying population polymorphism and unique evolutionary units, even within morphologically similar groups (Bitencourt et al, 2011;Utsunomia et al, 2014).…”