Allozyme variation and divergence in the phyllotine rodent Calomys hummelincki (Husson, 1960)

The aim of the present study was to assess the degree of genetic variation and divergence among six populations of Calomys hummelincki, a phyllotine r odent distributed in northern South America. With this information we will try to evaluate the two hypotheses of possible colonization and differentia tion of this group of rodents postulated by Baskin and Reig. We studied 34 loci by electrophoretic analysis: 21 were monomorphic for all populations a nd 13 were polymorphic in at least one population, being P-1% = 21.6% the m ean value for all populations. The mean value of heterozygosity per locus w as H = 0.075. Low values of genetic distance were observed among population s of the Llanos region (0.001 < D < 0.006). There was a larger genetic dist ance (D = 0.024) between the population from Isiro, in the northwestern sem iarid region, and those from the Llanos region. The insular population of A ruba displayed the lowest value of genetic distance with the population fro m Isiro (D = 0.014). The specimens from Sipao, on the right side of the Ori noco river, displayed the highest values of genetic distances in comparison with other populations of C. hummelincki (0.070 < D < 0.095). The relative ly high differentiation was due to the fixation of new alleles, not found i n other populations of C. hummelincki, at loci Idh-1 and Est-2. F-statistic s and Nm values indicated reduced gene flow among the populations sampled. Despite the limited data, the results seem to support Reig's hypothesis abo ut south to north colonization of genus Calomys in South America.