Data from: Oviposition site choice under conflicting risks demonstrates that aquatic predators drive terrestrial egg-laying

Laying eggs out of water was crucial to the transition to land and has evolved repeatedly in multiple animal phyla. However, testing hypotheses about this transition has been difficult because extant species only breed in one environment. The pantless treefrog, Dendropsophus ebraccatus, makes such tests possible because they lay both aquatic and arboreal eggs. Here, we test the oviposition site choices of D. ebraccatus under conflicting risks of arboreal egg desiccation and aquatic egg predation, thereby estimating the relative importance of each selective agent on reproduction. We also measured discrimination between habitats with and without predators and development of naturally laid aquatic and arboreal eggs. Aquatic embryos in nature developed faster than arboreal embryos, implying no cost to aquatic egg laying. In choice tests, D. ebraccatus avoided habitats with fish, showing that they can detect aquatic egg predators. Most importantly, D. ebraccatus laid most eggs in the water when faced with only desiccation risk, but switched to laying eggs arboreally when desiccation risk and aquatic predators were both present. This provides the first experimental evidence to our knowledge that aquatic predation risk influences non-aquatic oviposition and strongly supports the hypothesis that it was a driver of the evolution of terrestrial reproduction.Monitoring development of aquatic and arboreal frog eggsDevelopmental stage of aquatic and arboreal Dendropsophus ebraccatus embryos at approximately 16, 30 and 48 hours post-oviposition, in two ponds near Gamboa, PanamaDevelopment monitoring.csvPredator discrimination tests by Dendropsophus ebraccatusNumber of arboreal eggs laid by Dendropsophus ebraccatus in small tubs with and without fish.Predator discrimination tests.csvPredator Oviposition site choice trials by Dendropsophus ebraccatusNumber of aquatic and non-aquatic embryos and egg masses laid by Dendropsophus ebraccatus in the presence or absence of fish.Predator Oviposition site choice trials by pair.cs