The surface tension of water provides a thin, elastic membrane upon which many tiny animals are adapted to live and move. We show that it may be equally important to the minute animals living beneath it by examining air-breathing mechanics in five species (three families) of anuran (frog) tadpoles. Air-breathing is essential for survival and development in most tadpoles, yet we found that all tadpoles at small body sizes were unable to break through the water's surface to access air. Nevertheless, by 3 days post-hatch and only 3 mm body length, all began to breathe air and fill the lungs. High-speed macrovideography revealed that surface tension was circumvented by a novel behaviour we call ‘bubble-sucking’: mouth attachment to the water's undersurface, the surface drawn into the mouth by suction, a bubble ‘pinched off’ within the mouth, then compressed and forced into the lungs. Growing tadpoles transitioned to air-breathing via typical surface breaching. Salamander larvae and pulmonate snails were also discovered to ‘bubble-suck’, and two insects used other means of circumvention, suggesting that surface tension may have a broader impact on animal phenotypes than hitherto appreciated.
The localization, isolation and partial characterization of a collagenolytic enzyme from the land planarian Bipalium kewense is described. This enzyme can be obtained by direct extraction of the organism, and can be separated from non-collagenous proteolytic activity by (NH(4))(2)SO(4) precipitation and Sephadex-gel chromatography. Its mode of attack on collagen and sensitivity to a variety of inhibitors indicate that this enzyme differs from vertebrate collagenases and a previously described invertebrate collagenase.
We describe air-breathing mechanics in gray tree frog tadpoles (Hyla versicolor). We found that H. versicolor tadpoles 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 tadpoles bubble-suck throughout the larval period, despite reaching body sizes at which breaching is possible. Hyla versicolor tadpoles 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 tadpoles 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 bubblesucking represent two-and four-stroke ventilation systems, which we discuss in the context of other anamniote air-breathing mechanisms.
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