Nav: Home

How red-eyed treefrog embryos hatch in seconds

June 15, 2016

Enclosed in a case of moist jelly, most minute frog embryos take their time emerging from the protective coating; but not the spawn of tree dwelling Agalychnis callidryas (red-eyed treefrogs). When the eggs find themselves under attack by predatory snakes, the tiny embryos can burst out of their eggs in as little as 6s before dropping to safety in water below. 'This escape hatching is a mechanism for running away from a really important predator', says Karen Warkentin from Boston University, USA. But she was unsure how the tiny animals made their escape. Explaining that most frog embryos liberate themselves by releasing enzymes from hatching glands on their heads that slowly degrade the egg membrane, Warkentin thought that it was unlikely that treefrog embryos used the same approach, because the hatching process was so swift and the egg membrane remained largely intact. 'We had seen them thrashing around and we thought they were somehow breaking out of the egg', she recalls. So when Mark Seid at the Smithsonian Tropical Research Institute, Panama, got access to a high-speed camera, Warkentin grasped the opportunity to reveal the mysteries of the treefrog embryos' escape in fine detail. Warkentin and her colleagues publish their discovery that the escapologist embryos rapidly release egg membrane degrading enzymes from their snouts that digest a small hole in the structure that the tiny escapee can wriggle through to freedom in Journal of Experimental Biology at

Fortunately, Warkentin and Seid had no difficulties collecting newly laid frog spawn from a nearby experimental pond overhung with accessible foliage. The duo then allowed the eggs to develop for 5days before gently prodding them to trigger breakouts. 'One of the first and most interesting behaviours that we observed was shaking', recalls Kristina Cohen, who also noticed the embryos repeatedly opened and closed their mouths before the egg membrane ruptured. 'Following this... you see fluid start to leak from the location in the membrane that is just in front of the embryo's snout', says Cohen, who recalls how the embryo then plugged the rupture by lodging its snout against it, before wriggling through in a bid for freedom. The embryos had made a hole in the membrane without even touching it. 'Once we saw that, we thought it was probably enzymatic', says Cohen. But where was the enzyme being released from?

'We came up with this very low-tech experiment', says Cohen, describing how she spun the embryos around in the egg after they had been trembling and gaping for a few seconds to find out where the rupture formed: 'If you don't perform the manipulation at the right time it doesn't work', says Cohen. However, when she timed the rotation perfectly, a hole appeared in the membrane next to where the embryo's snout had been originally located. The embryos must be releasing enzymes from somewhere on their heads to liberate themselves from the egg membrane.

Searching for hatching glands over the surface of the embryos' heads with a scanning electron microscope, Cohen successfully located tightly packed clusters of the glands on the embryos' snouts. Then, she painstakingly collected detailed scanning transmission electron microscopy images of the cells from embryos before they hatched and images of tadpoles immediately after they had successfully broken out. 'Getting those images was indeed a lot of work', says Warkentin, recalling how Cohen's patience was eventually rewarded when the images revealed that the hatching gland vesicles had released their contents just seconds before hatching.

So, red-eyed treefrog embryos evade snake predators by rapidly releasing enzymes from hatching glands concentrated on the snout at one specific location to rupture the egg membrane and produce an aperture through which the embryo can wriggle in a matter of seconds in a life-and-death bid for survival.

REFERENCE: Cohen, K. L., Seid M. A. and Warkentin, K. M. (2016). How embryos escape from danger: the mechanism of rapid, plastic hatching in red-eyed treefrogs. J. Exp. Biol. 219, 1875-1883. DOI: 10.1242/jeb.139519

This article is posted on this site to give advance access to other authorised media who may wish to report on this story. Full attribution is required, and if reporting online a link to is also required. The story posted here is COPYRIGHTED. Therefore advance permission is required before any and every reproduction of each article in full. PLEASE CONTACT


The Company of Biologists

Related Embryos Articles:

Technology to screen embryos before implantation falls short
Because current methods for assessing the viability of IVF-created embryos are not sufficiently reliable, more research on embryo development is needed, two experts write in a new review article.
Researchers watch blood vessels develop in whole Zebrafish embryos
For the first time, researchers have followed the development of blood vessels in zebrafish embryos without using any labels or contrast agents, which may disturb the biological processes under study.
Friction shapes zebrafish embryos
The biochemical signals that give an embryo its shape have been studied extensively.
Handedness arises from genes in the spinal cords of embryos
The left side of the spinal cord matures slightly faster than the right side in human embryos of four to eight weeks age.
Scientists use stem cells to create human/pig chimera embryos
Efforts by Salk Institute researchers to grow the first embryos containing cells from humans and pigs proved more challenging than anticipated, they report in Cell.
Research on dinosaur embryos reveals that eggs took 3 to 6 months to hatch
New research on the teeth of fossilized dinosaur embryos indicates that the eggs of non-avian dinosaurs took a long time to hatch --between about three and six months.
Scientists improve predictions of how temperature affects the survival of fish embryos
NOAA Fisheries Ecology Division and UC Santa Cruz researchers found the thermal tolerance of Chinook salmon embryos in the Sacramento River is much lower than expected from laboratory studies.
Researchers put mouse embryos in suspended animation
UC San Francisco researchers have found a way to pause the development of early mouse embryos for up to a month in the lab, a finding with potential implications for assisted reproduction, regenerative medicine, aging, and even cancer, the authors say.
Scientists make embryos from non-egg cells
Scientists have shown for the first time that embryos can be made from non-egg cells, a discovery that challenges two centuries of received wisdom.
Frozen embryos more effective than fresh in women with polycystic ovary syndrome
Women with polycystic ovary syndrome who receive frozen embryos during in vitro fertilization have safer and more successful pregnancies than those who get fresh embryos, according to the results of a recent collaboration between Penn State College of Medicine and Chinese researchers.

Related Embryos Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Climate Crisis
There's no greater threat to humanity than climate change. What can we do to stop the worst consequences? This hour, TED speakers explore how we can save our planet and whether we can do it in time. Guests include climate activist Greta Thunberg, chemical engineer Jennifer Wilcox, research scientist Sean Davis, food innovator Bruce Friedrich, and psychologist Per Espen Stoknes.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...