Chromosomal polymorphism and speciation in Laetacara cf. dorsigera (Teleostei, Perciformes, Cichlidae) from the river Parana PR Brazil

摘要

Four sympatric and syntopic karyotype forms of Laetacara cf. dorsigera, centric fusion-originated were analyzed. Specimens with 2n=46, 2n=45, 2n=44 and 2n=43 chromosomes and differences with regard to the number of metacentric chromosomes, inversely proportional to their diploid number, were reported. Karyotypic formulae of the four cytotypes were: cytotype A=2M + 44A; cytotype B=3M + 42A;. cytotype C=4M + 40A and cytotype D=5M + 38A and fundamental number constant (NF=48). Two centric fusion events are suggested: a) Robertsonian translocation, which originated the first and second metacentric chromosomal pairs; b) isochromosome formed by the fusion of acrocentric homologous chromosomes in cytotypes with odd chromosomes. Genetic balance in the four karyotype forms of Laetacara cf. dorsigera seemed to have been determinant to their reproductive isolation. The presence of individuals with-different karyotypic structures living in sympatry and syntopy and the absence of "intermediate individuals" (recombinants), that would have been expected in a parimitic population, permit one to conclude that probably form 4 cryptic species exist in the population.