The widespread distribution of invasive species inevitably leads to the emergence of a new category of biotic relationships: interspecific predatory interactions between invasive species. We assessed the vulnerability of different life stages of the clawed frog, Xenopus laevis (eggs, hatchlings, tadpoles, newly-metamorphosed froglets, and adults), to predation by the Eastern mosquitofish, Gambusia holbrooki, and evaluated whether adult clawed frogs prey upon juvenile and adult mosquitofish. The results confirm differences in the palatability of different ontogenetic stages of the clawed frog by mosquitofish, as well as the low palatability of mosquitofish for adult frogs, with the exception of fish juveniles, which are relatively protected in the light but highly vulnerable under low-light conditions. Therefore, these fish-amphibian interactions are complex and can be defined as unequal bidirectional predation: the mosquitofish readily eliminates its early-stage opponent, but may become prey for its adult individuals. The revealed existence of a vulnerable mosquitofish stage makes it difficult to predict the unconditional suppression of clawed frog populations by this fish species when these two global aquatic invaders become syntopic in new regions. In any case, mosquitofish are likely to dominate in urban water bodies in locations with constant artificial lighting. We emphasise the importance of studying interactions at all ontogenetic stages, as well as taking into account the lifestyle of the organisms studied when analysing the mechanisms of predatory interactions between any pairs of invasive species in new areas of the planet.

Graphical abstract