Looking more closely: frog embryos  

Posted by Denis Haack in , ,

Scientist Karen Warkentin has been studying the eggs of tropical red-eyed tree frogs and has discovered that the embryos have survival skills prior to hatching.

Masses of these glistening eggs hang on leaves that dangle over tropical ponds, and the eggs stay put even when branches thrash in storms. A hungry snake biting into one end of an egg mass can make the embryos’ home dip and dance too. But at this jouncing, older embryos flee. They can’t run, but they can hatch. A sudden burst of emergency hatching sends a rain of new tadpoles into the water, often saving some 80 percent of a clutch.

In both events vibrations of the disturbance radiate through the clutch of eggs. Only the vibrations set up by the predator, however, triggers the early hatch. How the embryos can tell the difference is unknown.

Even from inside its egg, a remarkably young embryo can do a thing or two to get what it needs.

Among red-eyed tree frogs, Agalychnis callidryas, embryos develop big feathery gills for extracting oxygen from the watery world inside their eggs. But just where an embryo’s head-to-be lies within its egg makes a difference in oxygen availability. The part of an egg closest to the air typically carries twice the oxygen concentration of the deep interior squeezed among neighboring eggs, Warkentin and her student Jessica Rogge found. When Rogge prodded embryos so their gills fell into the low-oxygen zone, most of the 3-day-olds twitched themselves back into place within 15 seconds.

Rogge even tested embryos just a day old. “They don’t have blood. They don’t have a heart,” Warkentin says. They move only by beating a fuzz of tiny hairlike projections. Yet when Rogge nudged embryo front ends toward the downside of the oxygen gradient, more than half of the embryos she tested worked their fuzz to chug at least halfway back to the sweet spot within five minutes, she and Warkentin reported in 2008 in the Journal of Experimental Biology.

God has spoken in creation, word, and Word. These are not different words, but one, the word of God, and in each we catch a glimpse of his glory. None will come to an end, for his word is forever. Which is a good thing, because we’ll need plenty of unhurried time in the new earth to keep looking for glory.

Source: Science News (August 15, 2009) pp. 27-29, in a fascinating article, "Smart from the Start," you can read here.

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