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Keeping Reptiles Newsletter
Issue 23    
December, 2005
When snakes were venomous and lizards were not...
In this Issue

by Mark Chapple

When I was a boy there were only two species of venomous lizard, the Gila monster and the beaded lizard.


Gila Monster

When I was a boy there were only 250 known venomous snakes in the world. Most were harmless.

When I was a boy bearded dragons didn't have venomous rattlesnake toxins.

Not anymore.


Beaded Lizard

Books will have to be rewritten and web-sites republished after Bryan Fry, of the Australian Venom Research Unit at the University of Melbourne, and a team of international researchers have turned what we know of the history of snakes and lizards on its head over the past two years. Dr Fry has discovered that the number of venomous snakes in the world is not around 250 but actually closer to 2700.

He also discovered that a number of lizards, including iguanas, bearded dragons, goannas and komodo dragons are venomous. This new research indicates that when snakes first evolved 100 million years ago, their venom genes were already 100 million years old. Snakes, the researchers found, are closely related these lizards It's only among these lineages that the researchers have discovered venom. More distantly related lizards like geckos and skinks have no venom genes.


Komodo Dragon

Dr Fry said that because komodo dragons fed on carrion in the wild, bacteria in their mouths had long been blamed for the pain, swelling and prolonged bleeding that bites caused.

However, his doubts were raised after he saw a zoo keeper develop symptoms too soon after being bitten for the effect to be put down to bacteria. When he studied an Australian lace monitor, or common goanna, the closest relative of the komodo dragon, he found a gland running down the side of its jaw. Squeezing it released the venom. Dr Fry’s international team identified nine toxins in lizard venom that snakes also produce. One toxin found in the venom of the bearded dragon, one of the world's most popular pet lizards, had previously only been identified in rattlesnake venom.

But do not be alarmed bearded dragon, goanna and iguana lovers. Your pets' venom is only present in small amounts and unlike snakes; lizards have no fangs to inject the venom into their prey.


Lace Monitor

It is believe that venom systems in reptiles evolved only once about 200 million years ago, much earlier than had been thought, in a common ancestor of snakes and lizards.

‘The first venomous snake evolved from the heavy bodied swamp monsters similar to the anacondas of today. They needed a new tool to kill their prey since they were trading in the heavy muscle in order to become quicker and more athletic. Enter venom. They used this venom to feed on the cute little furry rodents that eventually became us.’, said Dr Fry.

“This origin of venom is so far back, that it occurred before the snake we commonly think of as ‘non-venomous’ even showed up on the tree of life. I realized that some of the ancient venom may still be produced by them today. So I started looking at non-venomous snakes. And when I looked at a ratsnake, the archetypal non-venomous snake, I isolated typical cobra-style toxin.”

"I just wanted to see how far back I could take snake venom," he said.

An international team of herpetologists collected cells from the mouth secretions of wild and captive lizards and cataloged the genes that were active in them.

After comparing these genes to those for snake venom they "isolated some rattlesnake toxins from the bearded dragons and started getting really excited," Dr. Fry said. As the research progressed it turned up venom genes in other species.

Dr. Fry and his colleagues found that the proteins encoded in these genes had the same effect as snake venom.

Whilst finding that lizards had similar venom was intriguing, it did not solve the question of how and when it evolved. Scientists have long debated which of the 4,750 species of lizards the closest cousins to snakes are.


Iguana - Costa Rica

These discoveries helped two of Dr. Fry's colleagues, Nicolas Vidal and S. Blair Hedges of Pennsylvania State University, who had been working on a large-scale DNA study. "We finally got enough data this year to resolve the problem," Dr. Hedges said. The venom came first, snakes later.

The research led to new ways of classifying reptiles based on their DNA and have found that the venomous snakes and lizards branch from the same point. They proposed a new name for these, Toxicofera - "those who bear toxins". This clade, or group, now includes serpentes (snakes), iguaninae (iguanas), varanidae (monitor lizards) and helodermatidae (Gila Monsters).

This discovery of the toxicity of many popular pet snakes is likely to send shockwaves through the international pet snake trade. Many non-venomous snakes, previously thought to have only mild ‘toxic saliva’, actually have true venom. Dr. Fry’s research has shown that some of the snakes common in the overseas pet market actually produce highly potent venoms.

This research highlights the misunderstanding that has often been the case with reptiles. In the late-70s/early 80s, some of the most popular snakes in the US pet trade were the Asian keelback snakes. It was only after several children were bitten and became severely ill that these snakes were found to be highly venomous.

“My research now shows that the vast majority of the snakes commonly kept as pets are actually venomous. Are all these species dangerous? Certainly not,” Bryan says.

‘Are there highly venomous species lurking in the petshops that we don’t know about? Definitely. I’ve consulted to two US petshops where employees were paralysed after being bitten snakes thought to be totally harmless.

The discovery may even cause a legislative storm in the United States and Europe.

However, it’s not all doom and gloom. Lizard venom may prove very useful in medicine. For some reason, the molecules in lizard venom are much smaller than those in snakes. Small molecules are less likely to be noticed by the immune system, meaning that they are less likely to cause allergic reactions.

Unfortunately, even as scientists discover these promising drug candidates, many of the lizards that produce them are threatened with extinction. "These animals that could potentially have the next wonder drug are literally getting wiped out before our eyes," said Dr. Fry.

References

NY Times
http://www.nytimes.com/2005/11/22/science/22venom.html?8hpib

New Scientist
http://www.newscientist.com/article.ns?id=dn8331

Penn State University
New paper of taxonomy of reptile and proposed new naming structure.
http://evo.bio.psu.edu/hedgeslab/Publications/PDF-files/171.pdf

Early evolution of the venom system in lizards and snakes
Dr Bryan Grieg Fry's Website
http://www.venomdoc.com/downloads/2005_BGF_Nature_squamate_venom.pdf

Toxicofera
http://en.wikipedia.org/wiki/Toxicofera

Shh! The Snake May Hear You

by John Carson

As reprinted in The Michigan Herpetologist, the newsletter of the Michigan Society of Herpetologists, September, 2001. Can snakes hear, you ask? A few decades ago the answer was no, for -- obviously -- snakes don't have external ears. And anyway, snakes don't appear to respond to loud noises. Further support for this view is found in some current zoology texts, which still report that snakes lack the sense of hearing.

But research begun about 35 years ago, especially the extensive investigations over many years by E.G. Wever and associates at Princeton University, has shown that snakes have a hearing capability (at least in an electro-physiological sense) comparable to that of lizards. This should not be too surprising, for snakes and lizards share some common features and are thought to have common ancestors.

So how can a snake hear, lacking external ears? By having equivalent structures on each side of its head. The skin and muscle tissue on each side of the head cover a loosely suspended bone, called the quadrate, which undergoes small displacements in response to airborne sound. The quadrate motion is transferred by intermediate structures to the cochlea, which produces electrical signals on its hair cells that correlate with the airborne sounds (within a range of intensity and frequency determined by the ear system) and are transferred to the brain. Cochlear signals are present in functioning ears of all classes of vertebrates from fish to mammals, while animals that are congenitally deaf produce no such signals, so their presence in response to sound is taken as an indication of the hearing sense.

Wever and co-workers [1] developed techniques to measure the hair-cell signals in lizards, snakes, and amphibians, which involved anesthetizing the specimen, inserting a very thin wire probe into contact with a hair cell, and measuring the acoustic signal level needed to produce a specified hair-cell signal (typically 0.1 microvolt). Various experiments were performed to demonstrate that the hair-cell signals were in direct response to airborne sound and not to mechanical vibrations from the medium on which the specimens were placed. According to Porter [2], the auditory response of snakes in the range of 200 to 300 Hz is superior to that of cats. Hartline and Campbell [3] investigated the transmission of airborne sound through the snake's skin and lung into the inner ear.

Wever's results show that this type of transmission, called the somatic mode, is much reduced compared to that through the skin to the quadrate, which is the main mode of hearing. How are the cochlear responses to be interpreted? Wever points out that it is often difficult to determine the role of hearing in lower forms such as reptiles. It is possible that snakes make less use of the auditory sense than other animals. He notes that the maximum sensitivity occurs in the frequency range of noise made by movements of large animals, so detection of such sounds could function as a warning to snakes to be motionless, a common defensive action with animals.

(Although not discussed in the references I was able to check, there is also the question of how the cochlear signals are used in the snake brain. Is it possible that the ability to process this information has been or is being lost?)

So the next time you meet a snake on the Reserve trails, be careful what you say to it, for the snake may hear you

References:

1. Wever, E.G. The Reptile Ear, Princeton University Press, 1978
2. Porter, K.R. Herpetology, Sanders Co., 1972
3. Hartline, P.H., and Campbell, H.W. "Auditory and Vibratory Responses in the Midbrains of Snakes" Science, Vol 163, 1221, (1969)

Reprinted with permission: Colorado Herpetological Society
Originally reprinted from the web site of the Torrey Pines State Reserve.

Turtle Stud Demand may Outstrip Supply

by Mark Chapple

The Great Barrier Reef Marine Park Authority is concerned that global warming is causing a rapid drop in the number of male sea turtles.

Male sea turtles are rather promiscuous creatures and are naturally outnumbered by the female of the species. But there are fears that the male turtles will be so outnumbered in future the species will fail to breed.

Fear that temperature rises are pushing up the temperature of turtle eggs as they incubate in sand. In natural conditions, the warmer the egg, the more likely the hatchling will be female. Females hatch if the egg is around 30 degrees, while 28 degrees produces a male.

While the natural population can be female-skewed, males obviously play a key role.
As you need both sexes to breed so you don't want temperatures getting too high and not having any male turtles produced.

Another concern is that predicted increases in extremely hot days will kill many turtles before they hatch. Temperatures of 33 degrees have already been noted on some turtle nesting spots. Just one more degree and the animals die.

Scientists are expecting a warming of at least 1.5 to 2 degrees this century. If greenhouse emissions are not cut, the warming could reach 5 degrees or more in the worst case scenario. This could be devastating to sea turtle populations around the world.

 

Petition for Rattle Snake Roundup

PLEASE, take a moment to sign onto this page to save the
rattlesnakes from some grisly, savage and cruel deaths. There
are now over 1400 signatures.

They need 10,000 signatures and you don't have to be a resident
of New Mexico to be counted. This is a fairly inhumane and
archaic practice that has been going on for many years and is
impacting on wild rattelsnake populations not only where it
takes place but also in nearby counties as they bringing
rattlesnakes in for the 'festivities'.

http://www.petitiononline.com/roundups

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Remember - there are lots of people who would love to hear your stories. Just e-mail me at: Reptile-Cage-Plans

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