Abstract
Hoplias malabaricus is a common fish species occurring in white, black and clear water rivers of the Amazon basin. Its large distribution across distinct aquatic environments can pose stressful conditions for dispersal and creates possibilities for the emergence of local adaptive profiles. We investigated the chromosomal localization of repetitive DNA markers (constitutive heterochromatin, rDNA and the transposable element REX-3) in populations from the Amazonas river (white water), the Negro river (black water) and the Tapajós river (clear water), in order to address the variation/association of cytogenomic features and environmental conditions. We found a conserved karyotypic macrostructure with a diploid number of 40 chromosomes (20 metacentrics + 20 submetacentrics) in all the samples. Heteromorphism in pair 14 was detected as evidence for the initial differentiation of an XX/XY system. Minor differences detected in the amount of repetitive DNA markers are interpreted as possible signatures of local adaptations to distinct aquatic environments.
Highlights
The rivers in the Amazon basin, South America, are usually categorized based on the appearance of their water color type
Vouchers were fixed in formalin 10%, preserved in ethanol 70% and stored in the Fish Collections of Instituto Nacional de Pesquisas da Amazônia (INPA) and Universidade Federal do Oeste do Pará (UFOPA)
The heterochromatic material around the telomeric region seemed to be slightly increased in the samples collected from black water (Figure 2c) than in those from white and clear water environments (Figure 2a, b)
Summary
The rivers in the Amazon basin, South America, are usually categorized based on the appearance of their water color type These rivers are recognized as white, clear and black water types (Goulding, 1997). Repetitive DNA represents a large portion of fish genomes and may play a role in genome structure maintenance, chromosomal physiology and possibly local adaptations processes (Charlesworth et al, 1994; Burt and Trivers, 2006). Such genomic elements are observed as tandem arrays (minisatellite and microsatellite sequences) or dispersed repeats (transposons and retrotransposons) (Martins, 2007)
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