Meeting Abstract
P2.108 Sunday, Jan. 5 15:30 Do distinct hatching glands mediate hatching at different ontogenetic stages in red-eyed treefrogs? COHEN, K.L.*; WARKENTIN, K.M.; Boston Univ.; Boston Univ. kcohen@bu.edu
Most anurans hatch by releasing proteolytic enzymes from hatching glands (HGs), transient, microvilliated cells on the head. In many species, HGs peak in abundance before hatching and continuously release enzyme, slowly degrading the membrane. Arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, hatch early to escape deadly flooding, dehydration, pathogens, and predators, with no prior general degradation of the membrane. In Gamboa, Panama, embryos hatch rapidly in snake and wasps attacks as early as age 4.4 d, cued by physical disturbance. Videos show localized membrane rupture at the snout seconds after stereotyped shaking behavior. We used strong hypoxia to probe the onset of hatching competence and electron microscopy to examine developmental changes in hatching glands. We observed hypoxia-cued hatching as early as 3.8 d, substantially before predator-induced hatching, within 15 min after flooding. We found two types of HGs that appear in different locations at different developmental stages. Small HGs with medium-length microvilli are widely distributed and abundant at the onset of hatching competence, but scarce in 5–6 d embryos. Large HGs with short microvilli become highly concentrated on the snout by 5 d, increase in abundance until hatching, then quickly regress. Scanning TEM revealed large HGs of unhatched animals to be full of secretory vesicles, but seconds after hatching these HGs had emptied at least half their contents; epithelial and ciliated cells were unchanged. These results suggest that A. callidryas use different mechanisms to hatch in different contexts and stages: small hatching glands that mediate relatively slow, very early hatching responses to hypoxia, and larger, more prominent hatching glands that enable rapid hatching to escape from predators at later stages.
