Gene flow in Trinidadian guppies

In 1957, guppies Poecilia reticulata from the Caroni drainage were introduced into habitat suitable for (but devoid of) guppies upstream of a waterfall in the Turure River of the Oropuche drainage. Previous allozyme studies, describing gene flow due to both sexes, showed that guppies downstream of the waterfall barrier represent an admixture of native and introduced genotypes. Using a polymerase chain reaction-restriction fragment length polymorphism assay of the highly divergent mitochondrial NADH2 gene only 12% of genotypes in the downstream population were shown here to correspond to the native matriline. The prevalence of introduced genotypes is discussed in the context of sexual conflict theory.