LAUSR

Dispersal is a fundamental determinant of species distribution and metapopulation structure, and freshwater species face strong challenges to disperse between hydrological catchments. Isolated freshwater lakes are inhabited by fish, posing the question of how were they colonized. It has often been proposed that fish dispersal to remote lakes can be facilitated by waterbirds, but there is no firm empirical evidence for such dispersal. We used field samples and experimental approach to demonstrate that eggs of two species of annual killifish are dispersed inside the digestive system of coscoroba swans in Brazil. An estimated one per cent of ingested killifish eggs were found to be viable in bird faeces and capable of continuing their development. Austrolebias minuano hatched after spending over 30 h inside a swan. Annual killifish eggs develop via diapausing stages that are primarily an adaptation to survive regular habitat desiccation and possess a thick chorion that may protect the eggs during their passage though the waterfowl gut, enabling such a unique form of fish dispersal. As well as being important over evolutionary time scales, this previously unknown dispersal mode may also be significant over ecological time scales, and explain surprising records of fish in closed-basin lakes and pools. This article is protected by copyright. All rights reserved.