Thursday, June 16, 2016

[Herpetology • 2016] How Embryos Escape from Danger: the Mechanism of Rapid, Plastic Hatching in Red-eyed Treefrogs Agalychnis callidryas


Red-eyed treefrog eggs Agalychnis callidryas hatching to escape from a cat-eyed snake Leptodeira septentrionalis
photo: Karen M. Warkentin NationalGeographic.com  DOI:  10.1242/jeb.139519

ABSTRACT

Environmentally cued hatching allows embryos to escape dangers and exploit new opportunities. Such adaptive responses require a flexibly regulated hatching mechanism sufficiently fast to meet relevant challenges. Anurans show widespread, diverse cued hatching responses, but their described hatching mechanisms are slow, and regulation of timing is unknown. Arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, escape from snake attacks and other threats by very rapid premature hatching. We used videography, manipulation of hatching embryos and electron microscopy to investigate their hatching mechanism. High-speed video revealed three stages of the hatching process: pre-rupture shaking and gaping, vitelline membrane rupture near the snout, and muscular thrashing to exit through the hole. Hatching took 6.5–49 s. We hypothesized membrane rupture to be enzymatic, with hatching enzyme released from the snout during shaking. To test this, we displaced hatching embryos to move their snout from its location during shaking. The membrane ruptured at the original snout position and embryos became trapped in collapsed capsules; they either moved repeatedly to relocate the hole or shook again and made a second hole to exit. Electron microscopy revealed that hatching glands are densely concentrated on the snout and absent elsewhere. They are full of vesicles in embryos and release most of their contents rapidly at hatching. Agalychnis callidryas' hatching mechanism contrasts with the slow process described in anurans to date and exemplifies one way in which embryos can achieve rapid, flexibly timed hatching to escape from acute threats. Other amphibians with cued hatching may also have novel hatching mechanisms.



Kristina L. Cohen, Marc A. Seid and Karen M. Warkentin. 2016. How Embryos Escape from Danger: the Mechanism of Rapid, Plastic Hatching in Red-eyed Treefrogs. Journal of Experimental Biology. 219: 1875-1883; DOI:  10.1242/jeb.139519

How red-eyed treefrog embryos hatch in seconds http://phy.so/385231208 via @physorg_com


 ABSTRACT: The life histories of many animals are characterized by niche shifts, the timing of which can strongly affect fitness. In the tree frog Agalychnis callidryas, which has arboreal eggs, there is a trade-off between predation risks before and after hatching. When eggs are attacked by snakes, tadpoles escape by hatching rapidly and falling into the water below. Eggs not attacked by snakes hatch later, when newly emerged tadpoles are less vulnerable to aquatic predators. Plasticity in hatching allows embryos to use immediate, local information on risk of mortality to make instantaneous behavioral decisions about hatching and the accompanying shift from arboreal to aquatic habitats.

K M Warkentin. 1995. Adaptive Plasticity in Hatching Age: A Response to Predation Risk Trade-Offs. Proc. Natl. Acad. Sci. USA.  92(8); 3507-3510. DOI: 10.1073/pnas.92.8.3507

Karen M. WARKENTIN. 2000. Wasp predation and wasp-induced hatching of red-eyed treefrog eggs. ANIMAL BEHAVIOUR. 60, 503–510. DOI: 10.1.1.540.2688

History of the Golfo Dulce Region, Costa Rica [Historia natural y cultural de la región del Golfo Dulce, Costa Rica] 


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