Eggs may not seem to do anything except sit around waiting to hatch, but the embryos inside them can do lots of behaving. That’s what undergraduate researcher Jessica Rogge of Boston University found after observing the directed movements of red-eyed treefrog embryos through the walls of their translucent, jelly-covered eggs. Rogge and Boston University associate professor Karen Warkentin found that even early on, the larval treefrogs wriggle around within their cramped quarters to find the “sweet spot” near the surface that is richest in oxygen.
When Rogge gently repositioned the embryos with a probe, turning the small bodies away from their oxygen banquet, the embryos quickly flipped themselves back into their favorite pose with gills fanned wide. Even the youngest embryos—without blood, gills, or muscles—would slowly cruise back into place.
Instead of depositing eggs in water, as most female frogs do, the red-eyed treefrog, an arboreal hylid native to Neotropical rainforests in Central America, lays her eggs on the underside of a leaf overhanging water. Tadpoles can hatch and drop into the water below just four days after the eggs are laid. But time is on their side—the longer they wait before hatching, the better equipped they will be to escape hungry mouths waiting in the water below.
Fact Source: http://accessscience.com/IOW/iow.aspx?iowID=40
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