THE POPULATION GENETIC-STRUCTURE OF CTENOMYS-PORTEOUSI (RODENTIA, OCTODONTIDAE)

Several aspects of the population biology and the population genetic structure of Ctenomys porteousi were studied. Chromosomal and allozyme polymorphisms in two local populations separated by 10 km were used to infer genetic structure. Heterochromatic addition/deletion rearrangements for six autosomal pairs were employed as genetic markers. Allozyme variants were analysed by the study of thirty-one presumptive loci. Thirteen loci (43%) were polymorphic, average observed heterozygosity per locus was 10%, and mean number of alleles per locus was 1.57. Chromosomal and allozyme frequencies were homogeneous across populations. The estimated F(st) values were very low, 0.009 and 0.022 for chromosomal and allozyme data respectively. Gene flow was indirectly estimated by the method of Wright, Nm values (mean number of migrants per generation per deme) was very high (27.2 and 11.3 for chromosomal and allozyme data respectively). The F(is) values suggest a significant defect of heterozygotes that could be explained by the Wahlund effect. The ecological data indicate the occurrence of sharp changes in density and in distribution pattern in short time. The genetic and ecological data suggest that the population structure of C. porteousi differs from that found in other species of Ctenomys affected by chromosomal mechanisms of speciation.