Meeting Abstract
Embryos of many species adaptively alter hatching timing in response to environmental cues. Most frogs hatch by secreting hatching enzyme from unicellular hatching glands (HG) on the epithelium, but mechanistic studies have not addressed the regulation of hatching timing. In many species HG peak in abundance long before hatching and secrete enzyme gradually, but we found that red-eyed treefrogs release enzyme only at the moment of hatching. Hourglass treefrogs, Dendropsophus ebraccatus, lay terrestrial eggs that hatch early to escape both dehydration and ant attacks. We study how D. ebraccatus accelerate hatching in both contexts, using an integrative framework to examine regulation at developmental, physiological, and behavioral levels. First, we split egg clutches into dry and well-hydrated treatments. Using scanning electron microscopy we found that, although eggs begin hatching after 70 h of development, HG in both treatments peak in abundance at about 32 h, then decline similarly. The pattern of HG abundance over time, plus our observations of gradual membrane degradation, indicate that enzyme secretion is gradual. However, in response to simulated ant attacks, embryos rapidly made a localized rupture in the membrane to escape. Scanning transmission electron microscopy revealed that HG are full of secretory vesicles before hatching, and depleted of vesicles just seconds after induced hatching, indicating acute release. We will also use qPCR to compare hatching enzyme expression and time-lapse photography to compare embryo behavior between hydration treatments. Although D. ebraccatus release enzyme gradually prior to spontaneous and dehydration-induced hatching, they can also release enzyme rapidly to escape from acute threats. Other anurans that exhibit gradual hatching enzyme release may also be capable of rapid release to escape acute threats.
