Frog Embryos Assess Danger

This image depicts 3-day-old embryos of the red-eyed treefrog species Agalychnis callidryas, taken in Gamboa, Panama. Although these embryos are not developed enough to hatch, they have well-developed external gills, which they position near the surface — the most oxygenated part of the egg. Doing this allows the tadpoles to maintain a high metabolic rate and rapid development, despite very low oxygen levels deeper inside their egg.  

Eggs like these often suffer high levels of predation, but were thought to be incapable of defending themselves. The recent discovery of amphibian embryos that hatch early to escape predators changed this view, and evidence for similar responses in fishes and spiders suggests that many embryos may respond adaptively to changing risks.  

In any life stage, appropriate responses to threat depend on the acquisition and processing of information, according to Karen Warkentin of Boston University. Her research on this treefrog species focuses on the mechanisms, evolution and ecological consequences of "adaptive plasticity" in life history switch points, particularly hatching. She is examining how the timing of their hatching is cued by environmental risks.  

The arboreal embryos of red-eyed treefrogs use vibrations in the egg mass to detect predatory snakes and wasps, and distinguish them from benign disturbances such as wind and rain. To characterize the sensory environment of embryos, Warkentin recorded the vibrations caused by important dangerous and benign natural disturbances, and standardized artificial disturbances. She then analyzed the recordings to determine which characteristics of the vibrations carry information that embryos could use to assess risk.

This study is revealing the rich sensory world and information processing abilities of embryos, and improving our knowledge of how animals use vibrational information.  The study will also improve the flow of information between behavioral biology and mechanical engineering to advance bio-vibrations research.

Warkentin's overall research program on adaptive plasticity of hatching in red-eyed treefrogs has been supported by the National Science Foundation at several stages, including a dissertation improvement grant, when she first discovered the plasticity, and two grants for her research as a member of the faculty at Boston University. She also received an NSF grant that focused on how embryos use vibrations to assess predation risk, and another NSF grant that addressed the ecological importance of plasticity across egg, tadpole and juvenile states.
 
For more information, read Snake Attack on Frog Eggs Provokes Premature Hatching: http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=104214&org=NSF.

- Diane Banegas, National Science Foundation

• New Amphibian Tree of Life
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