Geographic variation in genome size of Graomys griseoflavus (Rodentia : Muridae)

Studies on Thamomys and Peromyscus, among others, have confirmed that karyo typic variation in mammals is often reflected in genome size variation. We used flow cytometry to estimate genome sizes from 91 individuals of the kar yotypically variable Graomys griseoflavus complex from Argentina. Our sampl es represented 16 populations and included 2 ostensibly reproductively isol ated forms. The mean genome size (2C value) for all populations, 5.72 pg +/ - 0.34 SD of DNA, was low for mammals, and the range was greater than obser ved in previous studies on Geomys, Thomomys, and bats. Two groups of popula tions were identified that differed in mean genome size. A high-genome-size group consisted of 2 populations in San Juan Province with a mean genome s ize of 7.38 +/- 0.53 pg. These populations occupied the most arid part of t he Monte Desert. A small-genome-size group included the remaining 14 popula tions that mostly occupied a broadly distributed, continuous habitat and po ssessed lower genome sizes with a mean of 5.62 +/- 0.56 pg. Population mean s in this group ranged from 2C = 4.97 to 6.51. Previous studies have shown the existence of 2 reproductively isolated and karyotypically differentiate d species within the G. griseoflavus complex. The high-genome-size group se ems to correspond to the species with 2n = 42 (G. centralis) and the low-ge nome-size group to the species with 2n = 36-38 (G. griseoflavus). Flow cyto metry is a potentially useful method to rapidly assess differentiation amon g populations of the G. griseoflavus complex.