Meeting Abstract
The biomechanics of air-breathing in anuran tadpoles is virtually unstudied. Our previous work showed that surface tension prevents small tadpoles from breaching the surface to breathe. They overcome this constraint using a novel form of air-breathing, termed ‘bubble-sucking’. When bubble-sucking, a tadpole attaches its mouth to the under-surface of the water, expands its buccal cavity and pulls the surface into the mouth to create a bubble, which is then pinched off and compressed into the lungs. Tadpoles typically transition to breach breathing when large enough. In this study, we examined air-breathing mechanics in Hyla versicolor tadpoles over ontogeny using a combination of high-speed videography, paraffin histology, and statistical modeling. We found that H. versicolor differs from other species by never breach-breathing, even after growing large enough to do so. Rather, tadpoles transition from typical single bubble-sucks to ‘double bubble-sucks’, which entail an initial bubble-suck, during which the lungs are emptied and the bubble expelled, followed by a second bubble-suck, in which a second bubble is compressed into the lungs. Air remaining in the buccal cavity is released from the mouth. Unlike single bubble-sucks, double bubble-sucks prevent the mixing of fresh and used air, increasing the efficiency of air-breathing. The shift from single bubble-sucking to double bubble-sucking occurs at approximately 6 mm body length. At this same body length we found a parallel transition in lung morphology, shifting from a low to high degree of vascularization. These results suggest that single bubble-sucks in H. versicolor are non-respiratory, possibly serving developmental or hydrostatic functions, whereas double bubble-sucks provide a derived, efficient mechanism of gas exchange in H. versicolor.
