LSM1303 Animal Behaviour Student Blog : swallow

Honey, I Swallowed the Kids

LIM CHEE HAN — Fri, 21 Mar 2008 03:03:00 GMT

Images of mutated frogs have been stuck in my head for the longest time possible. I think I first came across them reading about pollution back in JC days. So while trawling the net for articles and images, I came across a more interesting article.

There's a species of frogs (Rheobatrachus silus), now thought to be extinct, that incubate their eggs in the STOMACH. The females swallows their fertilized eggs or tadpoles, shut down their digestive systems, and hatched their young in their stomachs. The young frogs secrete a certain hormones that halts the hydrochloric acid production in the female's stomach. About a month later the mother opened her mouth and regurgitated her tiny froglets. Imagine going on a one month fast!

Photo from Global Greenhouse Warming

Keith McDonald, the chief ranger with the Queensland Parks and Wildlife Service mentioned that it is possible to see the little frogs pushing their tiny hands and feet inside their mother’s swollen belly. *shudders*

Not unlike a case straight from the X-files, these frogs were discovered in the 1970s and vanished within 20 years. Apparently no one has seen any of them since. Some scientist speculates that a fungus, Chytrid, which is lethal to some amphibians is responsible for the extinction of the gastric-brooding frogs.

However, there remains a less "extreme" species of frogs known as....

Mouth brooders! Well, apparently there are species of frogs that incubate the young/tadpoles in their mouth. The Darwin's frog (Rhinoderma darwinii), which is also sometimes called Darwin's toad, is a pudgy frog with a triangle-shaped head that ends in a very pointy snout.

Photo from Wikimedia Commons

What happens is that the males stays with the eggs laid by the female and when they are about to hatch, scoops them into his mouth where they will slide into his vocal sacs. As the males now longer need any vocalization to attract females, the vocal sacs now provide a safe place for the eggs to incubate and hatch into tadpoles.

That's not all, after hatching, the tadpoles remain in his vocal sacs for a good 50 - 70 more days where they continue to grow into froglets! Imagine a very distented frog ambling along slowly.... Scientists speculates that the froglets survive via two means.

By slowly eating the leftover yolk from their eggs
As well as some food provided by the male's body through the skin lining his vocal sac.

The new froglets crawl out of the vocal sac, through their father's mouth, and to the outside, where they can begin hopping about on land.

These frogs kind of reminds me of those wooden russian dolls. Just.... a tad slimier.

References:

National Geographic, Victims of pollution, disease, and habitat loss, amphibians are vanishing all over the globe.
Vocal Sac-Brooding Frogs: Rhinodermatidae - Darwin's Frog (rhinoderma Darwinii): Species Account
University of Alabama, Chytrid Fungi Online
Global Greenhouse Warming, Gastric Brooding Frogs

Who says we need to chew our food?!

MUHAMMAD HAFIZ B ROSLEE — Tue, 18 Mar 2008 05:55:00 GMT

I remember getting an e-mail a few years back regarding a man-eating python! Besides that, there have been so many other stories about and photos showing snakes swallowing their unfortunate human victims, whole —THIS IS NOT FOR THE FAINT-HEARTED! There have been contentions as to whether snakes can really stuff food the size of the average man through their mouths but doesn’t that just make you wonder how big a snake’s jaw can expand to accommodate their feeding behaviour?

A king cobra with head raised

Photograph by Mattias Klum (Image retrieved from http://www.nationalgeographic.com/index.html)

I have to admit that I am extremely terrified of snakes. In spite of that I have always wondered how snakes swallow the animals they prey on whole, without having to chew them first. Even relatively smaller snakes like cobras do not chew their prey as they will just gulp the poor mouse down their ‘throats’. So I looked up National Geographic to check out some videos on these remarkable feats. It is really amazing!

There are generally two kinds of snakes—venomous and non-venomous. The former depend on their venomous fangs to immobilize their prey before feeding on them. The neurotoxins that are transferred into the bloodstreams of the prey paralyses them which would then facilitate these snakes to swallow the prey without any struggle from the latter. Venomous snakes include black mambas and cobras.

Close-up of a Black Mamba

Photograph by George Crall

(Image retrieved from http://www.nationalgeographic.com/index.html)

The non-venomous snakes on the other hand are usually bigger in size and they too immobilize their prey before they feed on the latter. However, this is through coiling around the victim, thus crushing the animals to death before swallowing them whole (like the anaconda in the previous National Geographic video), just like their venomous counterparts. Snakes like pythons and anacondas are usually bigger and stronger to enable them to wrest their victims still. However the most intriguing things here are how these snakes expand their jaws to a size comparable to that of their food.

Image retrieved from whiteafrican.com

Snakes’ jaws are unlike that of human beings whose upper jaw is “fused to the skull and therefore unable to move”. Snakes have jaws that are relatively more ‘mobile’ that are able to move both front-to-back and side-to-side. The bones connecting the upper and lower jaws of snakes work like ‘hinges’, thus allowing the lower jaw to “dislocate” and the mouth to gape. On top of that, the sides of the jaws of snakes are not fused together in the middle like our chins. Instead their ‘chins’ are made up of muscular tissues which facilitate the expansion of their jaws way beyond the initial size of their mouths. Read more about this and venomous fangs here.

(Diagram retrieved from How Snakes Work)

For a thorough scientific explanation on the mechanisms of the jaws of snakes, you can take a look at this research paper on the “Kinesis of the Jaw Apparatus during Swallowing in Cottonmouth Snake, Agkistrodon piscivorus” in JSTOR.

Not only do their jaws expand during feeding, but so do their hearts!

However, although it has been thought by all experts that all snakes swallow their prey whole, as was my initial perception; but recently it has been found that there is a kind of snake that eats “bite by bite”. More interestingly these snakes are found in Singapore!

References

“Ular Sawa Telan Manusia (Python Swallows Human)” by ‘sirloin skipper’. Fotopages, 10^th November 2006.
“Man Eating Python”. Black Bear Heaven.
“Different Types of Snakes” by Roy D’Silva. Buzzle.com, 5^th May 2007.
“How Snakes Work” by Lacy Perry. How Stuff Works: It’s good to know.
“Pythons Grow Bigger Hearst at Mealtimes” by James Owen. National Geographic News, 2^nd March 2005.
“Kinesis of the Jaw Apparatus during Swallowing in Cottonmouth Snake, Agkistrodon piscivorus” by Kenneth V. Kardong. JSTOR, 1977(2): 338-348.
"Snake eats its prey bite by bite". CNN.com/Sci-Tech, 10th July 2002.

Green Anaconda Devours The Spectacled Caiman Alligator!!! (Warning: Not for the faint-hearted)

CHUA CHING HOCK — Mon, 17 Mar 2008 19:16:00 GMT

Never thought that an adult Spectacled Caiman alligator (Caiman crocodilus) can be eaten alive by another predator? Well, think again!! Especially when you have this chap around:

(Image Source: http://animals.nationalgeographic.com/animals/reptiles/green-anaconda.html)

Introducing.... The Green Anaconda (Eunectes murinus) !!!

Well, I have always thought that anacondas' diet consist only of fishes, birds, rodents, mammals, and other small reptiles. But little did I expect to discover that this particular species, the Green Anaconda, actually feeds on full-grown Spectacled Caimans (which can grow up to 2.5m) as well!

Devouring a fellow fearsome predator? Wow.

My interest in inter-species conflict originally led me to stumble upon the incredible videos listed below. And upon closer research, I discovered that the Green Anaconda, located primarily in South America, is actually the largest snake in the world in terms of weight. They can grow up to 30 feet (9 meters) long, weigh 1,200 pounds (550 kilograms), and measure more than 12 inches (30 centimeters) in diameter.

Youtube Link:
http://www.youtube.com/watch?v=acVlIJeY9ws&feature=related

As illustrated in the video above, the Green Anaconda kills with power, not poison. By coiling its muscular body around its prey, the Green Anaconda can even crush the armoured Caiman until it can no longer breathe. This constriction tactic allows the Green Anaconda to take down other prey as large as adult capybaras (giant rodents), adult white-tailed deers, adult jaguars, and even humans of approximately 55kg or more.

At the same time, this brutal predator can be really covert and sleek in the water, with its dull colour and black blotches enhancing its camouflaging capabilities in the marshes and swamps. Its eyes and nasal openings are on top of its head, allowing it to wait and ambush its prey while remaining almost completely submerged.

Youtube Link:
http://www.youtube.com/watch?v=Xc06MVH6W98

Interestingly, while all the videos here highlight the Green Anaconda prevailing over the Spectacled Caiman, my research indicates that this is not always the case. In fact, renowned anaconda specialist Jesus Rivas once documented an intriguing event of the Spectacled Caiman preying on a green anaconda in return:

"On 25 of May 1996 we discovered a large caiman (>90 cm svl) firmly gripping the head of a radio-implanted female anaconda (494 cm TL, 29 kg), who in turn had wrapped herself around the caiman’s head and neck. After approximately 15 min the snake relaxed her coils, apparently losing the struggle with the caiman.

We interrupted the event to recover the transmitter when the snake stopped struggling. One of the teeth of the caiman had gone right through the skull and into the brain region, other tooth mark where present in the first fifth but did not look life threatening. The snake died two months later in captivity due to a generalized infection. As we had found this snake severely wounded from 2 months previous to being preyed on by the caiman, it is likely that she was not in top physical shape and this may have played some role in the attack."

Certainly, there appears to be a history of inter-species conflict between these two large predators. One possible reason could be due to the fact that both share very similar habitats in the seasonally flooded savannahs of South America and the Amazon Basin.

Youtube Link:
http://www.youtube.com/watch?v=KMwt_fEe3CY&feature=related
(Warning: Do not watch this if you just had a heavy meal.)

As seen in the fascinating video above, the Green Anaconda possesses jaws attached by pliable ligaments, which enables it to swallow the Caiman as a whole. Such a sizeable and yummy meal can allow it to go for weeks or even months without food.

At the same time, the Green Anaconda's unique adaptation and natural selection allow it to experience an incredible change in body size from birth to adulthood, as compared to other snakes. This explains how it can grow to such a massive bulk despite the occasional meal. Moreover, the role of nature has also dictated that baby Green Anacondas can almost immediately be able to swim and hunt once they are born. A top, ectothermic predator indeed.

Poor Caiman.

Finally, just to make you feel a little better, Green Anacondas are not known for being fond of attacking humans, despite their mythical reputation as man-eaters. Thankfully. =)

References:

BBC Science and Nature, Amazon Abyss (Apr 2005)
<http://www.bbc.co.uk/sn/tvradio/programmes/amazon/creatures.shtml> 16 Mar 2008

Isho, Fady D., AllExperts, Interspecies Conflict: Saltwater Crocodile vs Green Anaconda (26 Jan 2008)
<http://en.allexperts.com/q/Interspecies-Conflict-3754/2008/1/Saltwater-Crocodile-vs-Green.htm> 17 Mar 2008

Mayell, Hillary, National Geographic News, Anaconda Expert Wades Barefoot in Venezuela's Swamps (13 Mar 2003)
<http://news.nationalgeographic.com/news/2002/04/0430_020503_anacondaman.html> 16 Mar 2008

National Geographic, Green Anaconda
<http://animals.nationalgeographic.com/animals/reptiles/green-anaconda.html> 16 Mar 2008

Peach, Natasha, BBC Oxford, New Arrivals and Happy Feet (7 Jan 2008)
<http://www.bbc.co.uk/oxford/content/articles/2008/01/07/happy_feet_feature.shtml> 16 Mar 2008

Rivas, Jesus A., The Life History of the Green Anaconda (Eunectes murinus), with emphasis on its reproductive biology, Introduction (2000)
<www.anacondas.org/diss/intro.pdf> 17 Mar 2008

Rivas, Jesus A., Life history and conservation of the green anaconda - Eunectes murinus (2000)
<http://pages.prodigy.net/anaconda/research.htm> 16 Mar 2008

Rivas, Jesus A., Herpetological Review, Eunectes murinus: caiman predation (1999)
<http://pages.prodigy.net/anaconda/fight.htm> 16 Mar 2008

Rivas, Jesus A., Herpetological Review, Eunectes murinus: Juvenile predation (2001)
<http://pages.prodigy.net/anaconda/juvpred.htm> 16 Mar 2008

Vancouver Aquarium Marine Science Centre, AquaFacts: Green Anaconda - Eunectes murinus
<http://www.vanaqua.org/education/aquafacts/anaconda.html> 16 Mar 2008

Wikipedia, Anaconda (16 Mar 2008)
<http://en.wikipedia.org/wiki/Anaconda> 16 Mar 2008

Wikipedia, Green Anaconda (4 Mar 2008)
<http://en.wikipedia.org/wiki/Green_Anaconda> 16 Mar 2008

Wikipedia, Alligatoridae (10 Mar 2008)
<http://en.wikipedia.org/wiki/Caiman> 16 Mar 2008

Wikipedia, Spectacled Caiman (11 Mar 2008)
<http://en.wikipedia.org/wiki/Spectacled_Caiman> 16 Mar 2008