Parallel evolution of direct development in frogs - Skin and thyroid gland development in African Squeaker Frogs (Anura: Arthroleptidae: Arthroleptis).

Background: Cases of parallel evolution offer the possibility to identify adaptive traits and to uncover developmental constraints on the evolutionary trajectories of these traits. The independent evolution of direct development from the ancestral biphasic life history in frogs is such a case of parallel evolution. In frogs, aquatic larvae (tadpoles) differ profoundly from their adult forms and exhibit a stunning diversity regarding their habitats, morphology and feeding behaviors.