venom glands in lizards, komodo ect...

[SiUK]

Heres an extract taken directly from a thread on venomdoc, so credit goes to Dr Fry, I copied and pasted it because we are not allowed to post links to other rep forums.

Early evolution of the venom system in lizards and snakes
Nature doi:10.1038/nature04328

Bryan G. Fry (1,2), Nicolas Vidal (3,4), Janette A. Norman (2), Freek J. Vonk (5), Holger Scheib (6,7), S. F. Ryan Ramjan (1), Sanjaya Kuruppu (8.), Kim Fung (9), S. Blair Hedges (3), Michael K. Richardson (5), Wayne. C. Hodgson (8.), Vera Ignjatovic (10,11), Robyn Summerhayes (10,11) & Elazar Kochva (12)

1. Australian Venom Research Unit, Level 8, School of Medicine, University of Melbourne, Parkville, Victoria 3010, Australia.
2. Population and Evolutionary Genetics Unit, Museum
Victoria, GPO Box 666E, Melbourne, Victoria 3001, Australia.
3. Department of Biology and Astrobiology Research Center, 208 Mueller Lab, Pennsylvania State University, University Park, Pennsylvania 16802-5301, USA.
4. UMS 602, Taxonomie et collections, Reptiles-Amphibiens, De´partement Syste´matique et E´volution, Muse´um National
d’Histoire Naturelle, 25 Rue Cuvier, Paris 75005, France.
5. Institute of Biology, Leiden University, Kaiserstraat 63, PO Box 9516, 2300 RA, Leiden, The Netherlands.
6. Department of Structural Biology and Bioinformatics, University of Geneva and Swiss Institute of Bioinformatics, Centre Me´dical Universitaire, 1 Rue Michel-Servet, 1211 Geneva 4,
Switzerland.
7. SBC Lab AG, Seebu¨elstrasse 26, 8185 Winkel, Switzerland.
8. Monash Venom Group, Department of Pharmacology, Monash University, Clayton, Victoria 3800,
Australia.
9. Molecular and Health Technologies, CSIRO, 343 Royal Parade, Parkville, Victoria 3010, Australia.
10. Department of Pathology, University of Melbourne, Parkville,
Victoria 3010, Australia.
11. Murdoch Children’s Research Institute, Royal Children’s Hospital, Flemington Road, Parkville, Victoria 3052, Australia.
12. Department of Zoology, Tel Aviv University, Tel Aviv 69978, Israel.

Among extant reptiles only two lineages are known to have evolved venom delivery systems, the advanced snakes and helodermatid lizards (Gila Monster and Beaded Lizard)1. Evolution of the venom system is thought to underlie the impressive radiation of the advanced snakes (2,500 of 3,000 snake species)2–5. In contrast, the lizard venom system is thought to be restricted to just two species and to have evolved independently from the snake venom system1. Here we report the presence of venom toxins in two additional lizard lineages (Monitor Lizards and Iguania) and show that all lineages possessing toxin-secreting oral glands form a clade, demonstrating a single early origin of the venom system in lizards and snakes. Construction of gland complementary-DNA libraries and phylogenetic analysis of transcripts revealed that nine toxin types are shared between lizards and snakes. Toxinological analyses of venom components from the Lace Monitor Varanus varius showed potent effects on blood pressure and clotting ability, bioactivities associated with a rapid loss of consciousness and extensive bleeding in prey. The iguanian lizard Pogona barbata retains characteristics of the ancestral venom system, namely serial, lobular non-compound venom-secreting glands on both the upper and lower jaws, whereas the advanced snakes and anguimorph lizards (including Monitor Lizards, Gila Monster and Beaded Lizard) have more derived venom systems characterized by the loss of the mandibular (lower) or maxillary (upper) glands. Demonstration that the snakes, iguanians and anguimorphs form a single clade provides overwhelming support for a single, early origin of the venom system in lizards and snakes. These results provide new insights into the evolution of the venom system in squamate reptiles and open new avenues for biomedical research and drug design using hitherto unexplored venom proteins.

What all this means is that the dogma on the Discovery Channel about toxic bacteria being responsible for the bite effects produced by Komodo Dragons (and other monitor lizards) has been wrong. Its been a venom all this time!

In the course of this study, we worked out that snakes and lizards share a common venomous ancestor, rather than venom evolving independently. As part of this, we showed that the iguanian lizards retain the very very primative form of the venom glands, as shown by this picture of the Eastern Bearded Dragon



In constrast, the varanids have developed the lower jaw gland into a very complex venom gland. It is hollow, stores liquid venom and there are garden hose like ducts leading to the big teeth on the lower jaw. Even just gently squeezing the gland results in pooling of venom at the base of the teeth!



Key to understanding all of this is that these gland are not salivary glands. There is no homologous structure elsewhere in nature. The glands were evolved from the ancestral mucus secreting cells, changed to become protein secreting instead. This is what is present in the iguania. The snakes and anguirmorpha (anguiids, heloderms, varanids etc.) independently eventually ended up favoring different regions. The advanced snakes turned the maxillary (upper jaw) gland into the venom gland ubiquitous in advanced snakes while the anguimorphs developed the lower jaw. The iguanians haven't done much at all with it.

What we are doing now is investigating the role in prey capture. The delivery in varanids seems to be very efficient. Cool.

[davesadlerfunkaholic]

wow thats really cool, who knew lol

[Declan123]

so is it saying all lizards have some venom..?

[Cyberlizard]

I remember Wolfgang Wüster giving a related talk on this some years ago about their discovery that essentially far more colubrid snakes were, or in some cases are, venomous than was supposed.

That doesn't mean to say that toxic saliva isn't also present in the bite of the Komodo Dragon. Arguably, depending on which part of the jaw the Dragon uses to bite with, it may not deliver venom but still deliver the bacteria, since the latter is more likely to be spread around the whole mouth.

Anyone any comments?

[Cyberlizard]

PS I was thinking of a Dragon delivering an imperfect bite, rather than a 100% right-where-I-wanted-to-hit-you sort of bite.

[martin day]

wow so its all monitors then i always thought they had bacteria in the saliva that kept the wound from healing and causeing constant bleeding
do you know what the type of venom is called

[SiUK]

il try and get hold of the full paper and have a look.

[Steve]

Very interesting thanks for the post si

[carisma02uk]

ive seen this before and im sure you were there too.... was it this fourm? or a different one?
very interesting, i read the last one in more depth..
Jon

[SiUK]

yeah I think I might of posted it here along time ago, now I think about it.