ABSTRACT Invasive species affect ecosystems all over the world. Their impacts intensify when there are beneficial effects among different invasive species, an invasional meltdown. The Argentine black and white tegu lizard, Salvator merianae (Squamata: Teiidae), and the plant Eugenia uniflora (Myrtaceae) are native to mainland South America but behave as invasive species in other parts of the world. We tested the effectiveness of S. merianae as a seed disperser of E. uniflora. Tegu feces containing seeds of E. uniflora were collected to compare the seed germination of gut-passed seeds, manually de-pulped seeds, and seeds of whole fruits. Survival analysis indicated that Tegu lizards behave as seed dispersers of E. uniflora, and there was a tendency for gut-passed seeds to germinate faster than non-gut-passed seeds. Tegu lizards may carry seeds in their guts for considerable distances, facilitating the spread of E. uniflora where both species co-occur as native and invasive (e.g., southern USA). The results indicate a mutualistic interaction between the Tegu lizard and E. uniflora in their native range, which should be considered by initiatives to monitor and control the invasion of the lizard and the plant. world meltdown Squamata (Squamata Teiidae, Teiidae , Teiidae) Myrtaceae (Myrtaceae S E gutpassed gut passed depulped de pulped fruits nongutpassed non distances cooccur co occur e.g., eg e g (e.g. USA. USA . USA) range e.g. (e.g e.g