Comparative cytogenetics of Hoplias malabaricus (Pisces, Erythrinidae): a population analysis in adjacent hydrographic basins

Abstract

The chromosomes of specimens from four Hoplias malabaricus populations from headwaters of adjacent river basins at Ponta Grossa, southern Brazil, were investigated using differential staining techniques (C-banding, AgNO 3 and CMA 3 ) and fluorescent in situ hybridization (FISH) with an 18S rDNA probe. The diploid chromosome number in representatives of all four populations was invariably 2n = 42, with karyotypes composed of 12 pairs of metacentrics and 9 pairs of submetacentrics, without heteromorphic sex chromosomes. This kind of karyotype represents cytotype A in regard to cytotypes identified previously in H. malabaricus, exhibiting however, at the same time, some differences in the distribution of constitutive heterochromatin segments and in the locations of nucleolus organizer regions (NORs). The apparent karyotype similarity strongly suggests a close kinship among the studied populations, but the small differences detected in the examined chromosomal markers indicate some evolutionary divergence due to gene flow restriction among them.

Pleistocene karyotypic divergence in Hoplias malabaricus (Bloch, 1794) (Teleostei: Erythrinidae) populations in southeastern Brazil

“…Bi-telomeric NORs detected with silver nitrate were present in all samples, a characteristic trait for 2n = 42 trahiras within H. malabaricus Lemos et al, 2002;Vicari et al, 2003Vicari et al, , 2005. However, their frequency was sex-specific: they occurred in all 16 males, but only 14 out of 38 females, a sex bias unreported for other H. malabaricus populations.…”

Cytogenetic analysis and chromosomal characteristics of the polymorphic 18S rDNA in the fish Prochilodus lineatus (Characiformes, Prochilodontidae)

“…Size polymorphisms of the NORs are relatively common in Neotropical fishes (Foresti et al, 1981;Brum et al, 1998;Vicari et al, 2005) and are sometimes also associated with sex chromosomes (Galetti Jr., 1998;Molina et al, 1998;Born andBertollo, 2000, Artoni andBertollo, 2002;Vicari et al, 2003). Interestingly, a lethal effect in the rainbow trout (Oncorhynchus mykis) has been found to be related to a NORs size polymorphism in homozygotes, with evidence 622 Vicari et al also showing that heterozygotes present a higher adaptive value (Porto-Foresti et al, 2004).…”

Karyotype characterization, constitutive heterochromatin and nucleolus organizer regions of Paranaita opima (Coleoptera, Chrysomelidae, Alticinae)

“…These special types of heterochromatin flanking the NORs were not shown by the usual C-banding technique. The presence of constitutive heterochromatin flanking or inserting NORs has been found in the chromosomes of several different groups of animals (Cabrero et al, 1986;King et al, 1990;Pendás et al, 1993;Silva et al, 2000;Vicari et al, 2003Vicari et al, , 2005. The presence of this NOR-associated heterochromatin can restrict genetic recombination in the adjacent region, avoiding the formation of chiasmata or inducing their formation in other chromosome regions (John and King, 1982King, , 1985 and also can alter the genetic expression of the NORs (Arnold and Shaw, 1985) or can represent breakpoints that facilitate the dispersion of the NORs (Moreira-Filho et al, 1984;Reed Phillips, 1995).…”