Cytogenetics and karyosystematics of Oryzomys albigularis (Rodentia, Cricetidae) from Venezuela.

Several authors have proposed that Oryzomys albigularis constitutes a supraspecific complex and that chromosomal pericentromeric inversions have played a fundamental role in the diversifying process. With the purpose of clarifying the unclear taxonomic situation of the nominal forms of O. albigularis living in Venezuela, a cytogenetic study was carried out on individuals from five different localities along the Andean range and the Cordillera de la Costa. All of the individuals examined showed a diploid number (2n) of 66 chromosomes, but there were differences in the number of autosomal arms (FN = 90, 92, and 104) and in the morphology of the X chromosome (metacentric or acrocentric). The C-banding pattern was similar in all populations, autosomal heterochromatin was restricted to the centromere, and the Y chromosome was the only one that had completely heterochromatic arms. G-banding was useful in making arm-to-arm comparison between the FN = 90 and FN = 104 karyomorphs; 23 shared pairs were found, 7 pairs differed due to pericentric inversions, and 3 pairs had no correspondence. We postulate that these karyomorphs probably correspond to allospecies, and that the specific denominations must correspond to two previously recognized populations of sigmodontine rodents: O. caracolus Thomas 1914 (2n = 66, FN = 90), for the populations from the Cordillera de la Costa, and O. meridensis Thomas 1894 (2n = 66, FN = 104), for the populations distributed between the middle and extreme north of the Andean range. The specific denomination for the populations of animals from the southern portion of the Andean range (Oryzomys sp., 2n = 66, FN = 92) is still to be determined.