13.6 Wednesday, Jan. 4 The mechanism of rapid, plastic hatching in red-eyed treefrogs COHEN, K.L.*; SEID, M.A.; WARKENTIN, K.M.; Boston Univ.; Univ. of Scranton; Boston Univ. email@example.com
Although environmentally cued hatching is common and widespread in animals, including 12 families of amphibians, mechanistic studies treat hatching as a fixed developmental process. The treefrog Agalychnis callidryas can hatch in seconds up to 30% early in response to multiple risk cues, offering a robust model of plastic hatching. High-speed video of hatching shows a sequence of (1) mouth gaping and body tremulation, (2) presumably enzymatic vitelline membrane rupture, sometimes without physical contact, and (3) swimming movements by which embryos exit the egg. To assess the location and timing of hatching enzyme release and membrane rupture in relation to behavior, we cued embryos to hatch then turned some to a new position after tremulations began. Rupture was highly localized at the initial snout position. Turned embryos remained trapped in the collapsed membrane until they returned to the original rupture or tremulated again and made a second hole at a new snout location. In contrast to the gradual enzyme release and general membrane degradation described for other anurans, hatching in A. callidryas appears mediated by rapid, localized release of enzymes under behavioral control. We identified two candidate structures for a source of hatching enzymes. (1) Cells morphologically similar to described hatching glands are highly localized above the mouth, increase in prominence through the period of hatching competence, and disappear rapidly after hatching regardless of its timing. (2) The buccal roof of hatching-competent embryos stains positive with an antibody that marks hatching glands in Xenopus laevis. Elucidating the mechanism and control of the hatching process is necessary to understand the context and capacity for environmentally cued hatching.