Four-day-old embryos of red-eyed tree frog species Agalychnis callidryas, photographed in Gamboa, Panama.
These embryos are newly capable of hatching and will hatch rapidly if attacked by an egg-eating snake, or if their egg clutch is flooded (submerged under water), thereby reducing oxygen availability. If undisturbed, however, they will continue developing for about two more days in the egg, thereby improving their ability to escape from aquatic predators when they do hatch. The external gills, which they position in a small, well-oxygenated area just under the air-exposed surface of the egg, are critical for their ability to continue developing in the egg after reaching hatching competence. This image was taken as part of a research project examining how hatching timing is cued by risks. (Date of Image: 2005) [Image 4 of 5 related images. See Image 5.]
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The research is being conducted by Karen Warkentin of Boston University, and focuses on the mechanisms, evolution and ecological consequences of adaptive plasticity in life history switch points, particularly hatching. Warkentin is examining how the timing of hatching is cued by risks in A. callidryas. She is also studying related species--including some whose embryos respond differently to risk--in order to better understand how elements that contribute to hatching plasticity have evolved and the cumulative effects of plasticity across egg, larval and metamorph stages, to learn how fear and death combine to affect natural selection and population ecology.
Warkentin's overall research program on adaptive plasticity of hatching in red-eyed tree frogs has been supported by the National Science Foundation (NSF) at several stages, including a dissertation improvement grant, when she first discovered the plasticity, and two grants for her research as faculty at Boston University. She also received a grant from NSF's Division of Integrative Biology and Neuroscience (IBN 02-34439) that focused on the mechanisms of hatching plasticity, specifically on how embryos use vibrations to assess predation risk; and a grant from NSF's Division of Environmental Biology (DEB 07-16923), that addressed the ecological importance of plasticity across egg, tadpole and juvenile states.