The mechanics of air-breathing in gray tree frog tadpoles, Hyla versicolor LeConte, 1825 (Anura: Hylidae)

We describe air-breathing mechanics in gray tree frog tadpoles ( Hyla versicolor ). We found tha H. versicolor adpoles breathe by 'bubble-sucking', a breathing mode typically employed by tadpoles too small to break the water's surface tension, in which a bubble is drawn into the buccal cavity and compressed into the lungs. In most tadpoles, bubble-sucking is replaced by breach breathing (breaking the surface to access air) at larger body sizes. In contrast, H. versicolor adpoles bubble-suck throughout the larval period, despite reaching body sizes at which breaching is possible. Hyla versicolor adpoles exhibit two bubble-sucking behaviors: 'single bubble-sucking', previously described in other tadpole species, is characterized by a single suction event followed by a compression phase to fill the lungs; 'double bubble-sucking' is a novel, apparently derived form of bubble-sucking that adds a second suction event. Hyla versicolor adpoles transition from single bubble-sucking to double bubble-sucking at approximately 5.7 mm snout-vent length (SVL), which corresponds to a period of rapid lung maturation when they transition from low to high vascularization (6.0 mm SVL). Functional, behavioral and morphological evidence suggests that double bubble-sucking increases the efficiency of pulmonary gas exchange by separating expired, deoxygenated air from freshly inspired air to prevent mixing. Hyla versicolor , and possibly other hylid tadpoles, may have specialized for bubble-sucking in order to take advantage of this increased efficiency. Single and double bubble-sucking represent two- and four-stroke ventilation systems, which we discuss in the context of other anamniote air-breathing mechanisms.