Life in the wild is dangerous for baby animals, and when it comes to red-eyed treefrogs, the struggle to survive starts in the egg. Treefrogs lay their sticky eggs on broad leaves above tropical ponds, where they are vulnerable to many predators. However, the frog embryos have an escape strategy if a chomping snake appears: hatch prematurely and wiggle free. Boston University scientists have been studying red-eyed treefrogs for years, and now they’ve figured out just how the frog embryos abandon ship.
Karen Warkentin, professor of biology at BU’s College of Arts & Sciences, and her team previously discovered that frog embryos could hatch themselves early when they felt the vibrations of a predator attack. However, the embryos’ escape from their gelatinous eggs took only seconds, while normal hatching takes a lot longer. Clearly, the embryos were doing something different to burst out while they still had a chance to survive.
The secret, revealed in their latest study and published in June 2016 in the Journal of Experimental Biology, is enzymes. Warkentin, Marc Seid of the University of Scranton, and biology PhD student Kristina Cohen (GRS’17) used a high-speed camera and an electron microscope to watch and record as treefrog embryos broke free of their eggs. Startled by shaking that simulated an attack, the treefrog embryos trembled in their eggs, releasing enzymes from their snouts that dissolved a hole in the gooey shell. Then, they stuck their heads through and wiggled to freedom. Cohen took pictures of the embryos’ snouts before and after they escaped and showed that specialized cells holding the enzymes for hatching were full before the frogs burst out and empty afterward.
“This rapid…enzyme release allows red-eyed treefrog embryos to hatch at a moment’s notice across a broad developmental period,” says Warkentin. “It’s a critical part of a highly effective embryo self-defense mechanism.” When it comes to the red-eyed treefrog, it’s definitely survival of the fastest.
The research was funded in part by the Smithsonian Tropical Research Institute, where Warkentin conducts much of her fieldwork. Other funders include Boston University and the National Science Foundation.