MICROGEOGRAPHIC DISTRIBUTION OF ALLELE FREQUENCIES IN POPULATIONS OF CALOMYS-LAUCHA (RODENTIA, CRICETIDAE)

The microgeographic differentiation of allelic frequencies was analysed in two population samples of Calomys laucha, collected in a grid set in cultivated fields at Laguna Larga (Cordoba province, Argentina). One of the samples (n = 79) was obtained in May (autumn), when the population density is at a maximum, and the other (n = 85) in November (spring), at the onset of reproductive activity. F(ST) values for the November sample show significant differences between the six groups over which the sample was divided. F(IT) values show an excess of homozygotes for some loci in both samples. F(IS) reveals an excess of homozygotes within each of the groups. These results indicate the existence of subdivision in the population. Because C. laucha is a reservoir host of the Junin virus, an agent of endemic disease, this social organization may have epidemiological implications. Stratification of C. laucha populations into small breeding units could be one of the factors responsible for the high genic variability detected in this species.