title: Oviposition site choice under conflicting risks demonstrates that aquatic predators drive terrestrial egg-laying.
abstract: 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.
authors.affiliation: Department of Biology, Vassar College, 124 Raymond Avenue, Poughkeepsie, NY 12604, USA Department of Biology, Boston University, 5 Cummington Mall, Boston, MA 02215, USA jutouchon@vassar.edu.
authors.forename: Justin C
authors.initials: JC
authors.lastname: Touchon
authors.affiliation: Biology Department, Portland State University, 1719 SW 10th Avenue, Portland, OR 97201, USA.
authors.forename: Julie L
authors.initials: JL
authors.lastname: Worley
mesh_terms: D000818:Animals; D001001:Anura / Q000502:physiology*; D060126:Characidae / Q000502:physiology; D002755:Choice Behavior; D004777:Environment; D020387:Food Chain; D010058:Oviposition; D010176:Panama; D011235:Predatory Behavior
keywords: Anura; Neotropical; desiccation; oviposition site choice; predator avoidance; reproductive mode plasticity