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Estimated frequency of B-chromosomes and population density of Astyanax scabripinnis paranae in a small stream
Fábio Porto-ForestiI; Claudio OliveiraI; Edson Luis MaistroII; Fausto ForestiI
IDepartamento de Morfologia, Instituto de Biociências, UNESP, Campus de Botucatu, 18618-000 Botucatu, SP, Brasil and Centro de Aquicultura da UNESP. Send correspondence to C.O.
IIDepartamento de Biologia, Instituto de Ciência Químicas e Farmacêuticas, Universidade de Alfenas, 37130-000 Alfenas, MG, Brasil.
ABSTRACT
A study was made of the frequency of B-chromosomes and the population density of Astyanax scabripinnis paranae (Pisces, Characidae, Tetragonopterinae) from three stretches of the Cascatinha stream (Botucatu, SP). In the first stretch the population was estimated to be about 212 individuals and among 35 karyotyped specimens, 23 carried one macro B-chromosome; in the second stretch the population was estimated to be about 650 individuals and among 20 specimens karyotyped, two possessed one macro B-chromosome; in the third stretch the population was estimated to be about 107 individuals and among 10 specimens karyotyped, one carried one macro B-chromosome. A significant difference was observed in the frequency of macro B-chromosomes in females (57%) and males (8.7%) (P = 0.0001). These data suggest that the B-chromosome frequency and the populational density are not directly related. The hypothesis of the existence of some adaptive effect conferred by the B-chromosomes to the specimens from the first stretch of the Cascatinha stream is presented and discussed.
Keywords: B-chromosomes; population density; Astyanax.
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