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 http://jeb.biologists.org.

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.
-end-
IF REPORTING THIS STORY, PLEASE MENTION JOURNAL OF EXPERIMENTAL BIOLOGY AS THE SOURCE AND, IF REPORTING ONLINE, PLEASE CARRY A LINK TO: http://jeb.biologists.org/content/219/12/1875.abstract

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 jeb.biologists.com 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 permissions@biologists.com

THIS ARTICLE IS EMBARGOED UNTIL WEDNESDAY, 15 June 2016, 18:00 HRS EDT (23:00 HRS BST)

The Company of Biologists

Related Embryos Articles:

Turtle embryos play a role in determining their own sex
In certain turtle species, the temperature of the egg determines whether the offspring is female or male.
Early in vitro testing for adverse effects on embryos
ETH researchers have combined embryonic cells and liver cells in a new cell culture test.
Embryos' signals take multiple paths
Rice University bioscientists uncover details about how embryonic stem cells respond to the collection of signals that direct their differentiation into blood, bone and tissue.
Are mosaic embryos the 'dark horse' of IVF?
New research conducted by scientists at the Oregon National Primate Research Center at OHSU is the first to confirm in a nonhuman primate model, that mosaic embryos can adapt to their abnormalities and persist in development, resulting in positive IVF outcomes.
Embryos' signaling proteins go with the flow
Protein signaling in the rapidly differentiating cells of embryos is far more complex than previously thought, as pathways take cues from many other players.
More Embryos News and Embryos Current Events

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

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...