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= poisonous or venomous (seltsamer Titel

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Angelehnt an eine Diskussion in einem englischsprachigen Forum

Es wurde nach giftigen Reptilien gefragt, die ihr Gift zur Verteidigung einsetzen. Es gibt bekanntermaßen einige Amphibien z.b. Dendrobaten oder Molche, die aktive Hautgifte (z.b. TTX | ähnlich dem bekannten Kugelfischgift des FUGU ) zur Verteidigung einsetzen.
Bei Reptilien hingegen sieht es anders aus. Einige Arten sie zwar giftig|venomous , haben aber keine passive Verteidigung, wie Frösche | poisonous. Leider fiel ich auch kurz den beiden Begriffen zum Opfer, da im deutschen beides mit giftig übersetzt werden kann, sprachlich aber deutlich voneinander abgesetzt ist.

Lange Rede.

Eine Ausnahme hier stellt Rhapdophis spec. da, diese außergewöhnliche Gattung besitzt die Fähigkeit aktiv ein Opfer (auch Menschen) zu töten, wie auch passiv zur Verteidigung. Es handelt sich um verschiedene Toxine, die auf verschiedene Arten wirken.
Die Gattung Thamnophis, insbesondere einige lokale Populationen sind mittlerweile resistent , nicht immun, gegen das starke Gift TTX. Es hat sich eine Art "Wettrüsten" zischen den Molchen als Ernährung und den Prädatoren stattgefunden.

ttx = Klick

Alles in allem ein interessantes Gebiet

Beitrag 2, Verfasst am: Mi Feb 10, 2010 17:05 Titel:

Wenn ich mal wieder widerliche Eigenwerbung machen darf: das Thema giftig-giftig hab ich auf der Rhabdophis tigrinus formosanus-Seite auf www.snakesoftaiwan.com (geht nächste Woche online) wie folgt behandelt. Vielleicht wohnt ja irgendwo wer, den dat interessiert

This species is....the only known snake that is venomous and poisonous at the same time. (For the difference between "venomous" and "poisonous" see footnote (2)).

Here's how:

POISON:

The defensive behavior of this snake is very unusual. "When threatened by a predator, the snake arches its neck toward the attacker and releases the contents of paired nuchal glands that lie in the dorsal skin. The product of those glands is distasteful and irritating to the eyes and contains compounds similar to those found in the skin glands of toads." (Source)

The origin of the poison in these glands is a highly interesting aspect of this species, and was explained for the first time by a 2007 study by Hutchinson et al. The study shows that Rhabdophis tigrinus becomes poisonous by sequestering toxins from its prey which consists of venomous toads. The process allows the snakes to store in their neck glands some of the toxins from the toads they have eaten:

"Analyzing differences between snakes living on toad-rich and toad-deficient islands in Japan, researchers lead by Deborah A. Hutchinson of Old Dominion University in Norfold, Virginia, found that the Japanese grass snake or Yamakagashi, as the snake is known locally, did not manufacture its own venom, but instead relied on that found in toxic toads: the researchers found that snakes living on Japan’s toad-free island of Kinkazan lacked the toad’s toxic bufadienolide compounds completely. Snakes from Ishima, where toads are plentiful, had high levels of bufadienolides. R. tigrinus from Honshu, where toad numbers vary, displayed a wide range of bufadienolide concentrations. Feeding R. tigrinus hatchlings toad-rich and toad-free diets confirmed these results.

The study also found that snake mothers with high concentrations of the toxin are able to pass bufadienolide toxin on their offspring helping protect them from predators. The Yamakagashi stores the sequestered toxins in 'a series of paired structures known as nuchal glands in the dorsal skin of the neck,' according to the researchers. When threatened the snake takes a defensive position that exposes the toxin-containing nuchal glands to predators.

While sequestering defensive toxins from prey is unusual among terrestrial vertebrates it is not unknown. Research published last year by Valerie C. Clark of Cornell University showed that poison dart frogs (Dendrobates species) and their Madagascar counterparts, the Mantella frogs, sequester toxic skin chemicals, called alkaloids, from the ants they eat. These alkaloids protect the frogs from predation. Similarly, some garter snakes are known to store tetrodotoxin from ingested newts while birds in New Guinea appear to sequester poisons from insects." (Source)

The NewScientist notes:

What is more, when attacked, snakes on different islands react differently. On Ishima, snakes stand their ground and rely on the toxins in their nuchal glands to repel the predator. On Kinkazan, the snakes flee. 'Snakes on Kinkazan have evolved to use their nuchal glands in defence less often than other populations of snakes, presumably due to their lack of defensive compounds,' says Hutchinson. Moreover, baby snakes benefit too. The team showed that snake mothers with high toxin levels pass on the compounds to their offspring. Snake hatchlings thus also enjoy the toad-derived protection.

More details on this study can be found here. The study itself, 'Dietary sequestration of defensive steroids in nuchal glands of the Asian snake Rhabdophis tigrinus' by Deborah A. Hutchinson, Akira Mori, Alan H. Savitzky, Gordon M. Burghardt, Xiaogang Wu, Jerrold Meinwald, and Frank C. Schroeder" is available here.

VENOM:

Many members of the family Colubridae that are considered venomous are essentially harmless to humans, because they either have small venom glands, relatively weak venom, or an inefficient system for venom delivery. While Rhabdophis tigrinus has small venom glands and delivers its venom inefficiently, said venom is certainly not weak. Although this snake is reluctant to bite defensively, the bite has been known to cause fatalities in humans. The venom acts very slowly, inhibiting the ability of the blood to clot and causing death by hemorrhage:

"Three cases of serious envenomation by this species are reported (in Japan), all marked by delayed, spontaneous, superficial hemorrhaging and profound impairment of normal blood coagulation. In two cases these phenomena were accompanied by signs of severe internal hemorrhaging and hemolysis. Other symptoms may have resulted from transitory involvement of the central and autonomic nervous systems. Therapeutic measures applied in these cases are described, including the apparently effective use of a systemic antihemorrhagic drug. It is concluded that R. tigrinus is a dangerously venomous snake and potentially lethal to man." (Source)

For this reason, "the small colubrid snakes of the genus Rhabdophis have a shady past in the pet trade. Because they resemble certain harmless garter-snake like species, they were imported into the U.S. and U.K. under the wrong names, and ended up causing medically-significant emergencies when they bit their new owners." (Source)

FOOTNOTE (2)

(2) "The distinction between venom and poison

There is a difference between organisms that are venomous and those that are poisonous, two commonly confused terms applied to plant and animal life:

- Venomous...refers to animals that deliver (often, inject) venom into their prey when hunting or as a defense mechanism.

- Poisonous, on the other hand, describes plants or animals that are harmful when consumed or touched. A poison tends to be distributed over a large part of the body of the organism producing it, while venom is typically produced in organs specialized for the purpose" (Source)

Beitrag 3, Verfasst am: Mi Feb 10, 2010 17:25 Titel:

Du liest wohl auch mit

Sag bescheid, wenn Du online bist.

Beitrag 4, Verfasst am: Do Feb 11, 2010 4:00 Titel:

Ich bin immer online zwischen 03:00 und 15:00 deutscher Zeit......fallls das an mich gerichtet war