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.
Highlights
The ichthyofauna from coastal hydrographic systems in Eastern Brazil presents a remarkable biogeographic significance
In spite of the great number of chromosomal reports in fishes from South and Southeastern Brazil and, more recently, from Amazon basin, little is known about the cytogenetic features of species from Northeastern region (Medrado et al, 2008; Jacobina et al, 2009)
Silver nitrate staining revealed single nucleolar organizer regions (NORs) located at terminal regions on long arms of the second metacentric pair in both populations (Fig. 1, detail)
Summary
The ichthyofauna from coastal hydrographic systems in Eastern Brazil presents a remarkable biogeographic significance. Biodiversity studies depend on information about intra and interpopulation variability levels and characterization of evolutionarily significant units. In this sense, cytogenetic analyses represent a useful tool for conservation genetics, mainly of taxonomically controversial groups, once they can reveal population polymorphisms, discriminate cryptic species and cannot be replaced by DNA studies (Allendorf & Luikart, 2007). In spite of the great number of chromosomal reports in fishes from South and Southeastern Brazil and, more recently, from Amazon basin, little is known about the cytogenetic features of species from Northeastern region (Medrado et al, 2008; Jacobina et al, 2009)
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