Metamorphosis of behavior in the bullfrog (Rana catesbeiana)

This study describes the development of different spontaneous and elicited behaviors of frogs and their relationship to morphological, physiological, and ecological changes of metamorphosis. Tadpoles were studied at all stages of development from Stage XVIII, the onset of metamorphosis, to Stage XXV, when metamorphosis of the froglets is complete. Behaviors examined included development of forelimb postural support, postural responses to vestibular stimulation, the hindlimb withdrawal reflex, the corneal reflex, ocular mobility, and habitat preference. Results showed that these behaviors differ markedly in their timing and rate of maturation. Forelimb postural support and postural responses to vestibular stimulation improved gradually between Stages XX and XXV. In contrast, the threshold of the hindlimb withdrawal reflex remained essentially unchanged until Stage XXV, when it increased suddenly and dramatically. The corneal reflex appeared suddenly at Stage XXI with a threshold similar to that of juvenile frogs. The ability to move the eyes in response to visual or vestibular stimulation was pronounced in tadpoles, but gradually declined between Stage XVIII and Stage XXV, so that froglets showed almost no ocular mobility. The preference of metamorphosing frogs for deep water, shallow water, shoreline, or land were examined in an aquarium during a 24-hr observation period using time-lapse videotape recordings. Results showed that tadpoles spent progressively less time in deep water and shallow water as metamorphosis proceeded. Preference for land emerged suddenly at Stage XXII and remained high thereafter. There were no stage-related differences in preferences for the shoreline.