OLIGORYZOMYS FLAVESCENS (RODENTIA, MURIDAE) - GENE FLOW AMONG POPULATIONS FROM CENTRAL-EASTERN ARGENTINA

In species acting as hosts of infectious agents, the extent of gene fl ow between populations is of particular interest because the expansion of different infectious diseases is usually related to the dispersal of the host. We have estimated levels of gene flow among populations o f the sigmodontine rodent Oligoryzomys flavescens, in which high titer s of antibodies have been detected for a Hantavirus in Argentina that produces a severe pulmonary syndrome. Enzyme polymorphism was studied by means of starch gel electrophoresis in 10 populations from the area where human cases of Hantavirus have occurred. Genetic differentiatio n between populations was calculated from F-ST values with the equatio n Nm = [(1/F-ST) - 1]/4. To assess the relative importance of current gene flow and historical associations between populations, the relatio nship of population pairwise log Nm and log geographic distance was ex amined. Low F-ST (mean = 0.038) and high Nm (15.27) values suggest hig h levels of gene flow among populations. The lack of an isolation by d istance pattern would indicate that this species has recently colonize d the area. The northernmost population, located on the margin of a gr eat river, shows very high levels of gene flow with the downstream pop ulations despite the large geographic distances. Passive transport of animals down the river by floating plants would promote unidirectional gene flow. This fact and the highest mean heterozygosity of that nort hernmost population suggest it is a center of dispersal within the spe cies' range.