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Completed Project

Quantifying Variation in Reproductive Mode Plasticity in Dendropsophus ebraccatus

Hubert Szczygiel ’18, Anne Innes-Gold ’18, Phoebe Reuben ’17, and Justin Touchon (Biology)

Hourglass tree-frogs (Dendropsophus ebraccatus) shed light on the transition of vertebrates from aquatic to terrestrial environments because they can choose between laying their eggs above or below water. Laying eggs above the water protects them from aquatic predators and allows for increased gas exchange, but puts them at risk of desiccation and terrestrial predators. Laying eggs in water ensures ample hydration, but vastly increases predation risk. Understanding how these selective pressures affect egg-laying decisions can be used to understand the conditions under which extant terrestrially laying species evolved. Previous studies have shown that in open environments, females lay the majority of their eggs aquatically, presumably because of the high risk of desiccation in such environments. We tested 43 pairs of these frogs, collected from sites around Gamboa, Panama, and placed overnight in mesh cages partially submerged in pools of water in an open field. The following morning, we recorded the number of eggs laid and their locations above or below water. The number of eggs laid showed no correlation with female post-oviposition mass or snout-ventral length. On average, females laid approximately 50% of their eggs in water, and 50% above. However, egg deposition site varied considerably, from entirely aquatic to entirely terrestrial, even among females caught on the same night and exposed to the same atmospheric conditions. Thence, if such variation in reproductive behaviour has a genetic basis, then D. ebraccatus have the potential to be a model for studying the evolution of reproduction.