Toxins in Gray Treefrog Metamorphs

[John]

You know, I'd have to go and do a serious literature search for you to get specific papers, but there have been _many_ studies (we're talking hundreds of journal articles) done on amphibian toxicity, particularly in North American species of amphibian. This includes the toxicity of different stages in the life cycles. I'm quite sure Gray Tree Frogs feature in several.

As for significance medically and ecologically, that's nothing new - as well as biological research, there are billion dollar corporations doing drug screening based on natural products that come from everything from poison dart frogs to hydrothermal vent tube worms.

Regarding whether the snakes dying is a local phenomenon, Prof. Edmund "Butch" Brodie Jr has studied in incredible depth another member of the Thamnophis genus on the west coast, and different populations have different resistance to amphibian toxins. I don't have a citation to hand but I'm pretty familiar with his body of work (I've communicated with him several times actually). I don't think it's an unreasonable assumption that where ribbons are sympatric with Gray Tree Frogs they have some resistance to their toxins. That pretty much means you can't use these frogs to feed your snakes without at least some risk.

Butch's research has shown that while the snakes are resistant to amphibian toxins, they are not immune to them. I'm pretty sure metamorph Gray Tree Frogs have particularly high levels of toxins in them as a way to discourage predation of metamorphs leaving ponds. Combine this with the fact that the snakes are resistant rather than immune, and it seems quite reasonable to me that the younger snakes would be more likely to die in your scenario.

On another note, you're probably not going to win any friends here by posting about feeding amphibians to snakes. After all, this is a forum for people who keep amphibians as pets. Ribbon snakes certainly don't need to eat amphibians - they will eat insects, and insects are a heck of a lot more abundant than amphibians. So don't be surprised if you get some unhappy responses on this topic.

Best,

John

[opistoglyph]

Thanks for the fast response.

No I realize I won't win friends with this, but I've devoted acres of my land to local wildlife, including introducing colonies of local amphibians, and I keep a few dozen species of amphibians as well. I only feed the amphibians (from my own ponds, not wild caught) to snakes that haven't been switched to scented food yet, and have fed plenty of small abundant captive born local snakes to my larger amphibians, so it evens out. I even witnessed a large bullfrog make the mistake of grabbing the head of a big watersnake that was swimming by with only the head visible. Boy were THEY both surprised!

Just like frogs. You can't buy Purina Snake Chow, they gotta eat what they eat..

Reminds me of people calling me to complain about a hawk at their bird feeder eating their birds. First of all, not YOUR birds, second, a Hawk IS a bird. You've constructed a food chain, lol! Third grade, 101.

Mostly posted out of curiosity as to whether others have noticed this kind of toxicity variance in various stages, and also as kind of a warning. Until I got a concentrated dose of stressed gray treefrog poison in me, I had NO clue they could be that toxic- I've handled them for years without any serious effects. I'm usually more careful.

[SkeletalFrog]

It's just a poster from a meeting, but this might be what you're after: Comparative Peptide Profiles of Sympatric Anurans Hyla versicolor (Hylidae) and Lithobates clamitans (Ranidae): An Anti-predator Hypothesis

The above study was done with adults, but this study compared palatability between species, and found most amphibians tested would eat H. versicolor tadpoles with no reported ill effects.

Another possibility to consider - could that pond containing the tadpoles have been contaminated with anything recently? Given how you describe your land, my reflexive suggestion is local kids sneaking out there at night and accidentally/deliberately dropping something into the pond.

[opistoglyph]

Thank you for the links!

On the possibilty of pollutants, kind of slim. The amphibians in the pond, plus the uneaten metamorphs from the cage are all acting healthy. Plus, people sneaking on MY property? I was the biggest breeder of venomous snakes in the northeast for 20 years. Everyone around here is convinced that I keep stuff running around loose in my yard (don't know WHO would start rumors like that!) for protection. When I had the big mammals and valuable birds, I had a perimeter fence, now I don't even need one- paranoia does the trick. Scared neighbors are good neighbors.

No sign of illness in the one survivor from that group of babies, or other babies from different groups that didn't eat yesterday. I might try a couple of survivor metamorphs on a couple baby watersnakes and see the result- which wouldn't be conclusive being a different species and all, just interesting to note..

[LilyPad]

Why would you continue to "experiment" and kill off more snakes when you saw the results of the first round? I'm not a expert in reptiles and amphibians, and I agree that it is odd you would post this on a forum where frogs are beloved pets, but just coming from a rational, common sense standpoint, why would you want to kill more snakes in such a traumatic way?

[opistoglyph]

These same snakes, had they not been born in a cage in my collection, would have been born on my property and eating the same foods. Observation wise, it would be interesting to note whether the same toxicity problem is noted in Natrix in the same location as the Thamnophis. Both Thamnophis and Natrix have dozens to a hundred young apiece, and 99% die in the wild in their first few weeks, much like amphibians.

And when do the toxin levels change or drop? Or the tolerances of the predators build up to suitable levels? The whole concept that amphibian toxins change at various stages is brand new to me after 52 years in this field, and I'm willing to bet others that read this may find it interesting. Much less the fact that a severely road injured gray treefrog could pump out enough toxin to incapacitate a 200 lb man capable of surviving black forest cobra bite without antiserum, (plus the other nasty effects I had from it).

There have been many recent years when both ribbons and watersnakes had very low populations, most had presumed predation by night and blue herons, much like half the turtles in the US that are disappearing, as well as many amphibians. These birds are at pest levels now. If the problem actually relates to a change in toxins in young treefrogs locally, it certainly would be interesting to note it. This is not the first time I've raised these species and fed them wild caught food before they got large enough to switch over to scented pinkies, and I'm almost certain gray treefrog metamorphs were in the mix, so this is kind of interesting to me and local wildlife people. Our state people know almost nothing about amphibians or reptiles.

I have entomologist friends who object to my feeding insects to my amphibians as well, including species thought previously to be toxic that are accepted quite well. I know many amphibian people who feed pinkie mice to large salamanders and even larger mice to various frogs (though they are not acceptable as a regular diet item and may be bad for them, the hobbyists often brag about it). Many people like mice. I know many people who feed feeder fish of several species to amphibians. Many people like fish.

Wasn't looking for sympathy or approval, just intellectual dissemination. I see pictures of people with treefrogs on their faces, handled by their children, and think back to my stressed gray treefrog accidental toxin ingestion and shudder. If the young are more toxic or have a different toxin, that might be handy for hobbyists to know. Some keepers of aquatic salamanders load their tanks up with tadpoles for food- might save them a loss of a valued specimen. Likewise, a lot of reptile enthusiasts are also members here, and it might be a cautionary tale for them as well.

And lastly, the few specimens of extremely numerous amphibians and reptiles Iwould sacrifice in the pursuit of this knowledge are nothing compared to the deaths of thousands of larval amphibians kept and raised by hobbyists who have never bought a water test kit or studied filtration or understood oxygenation of the container and population dynamic who are thrilled to have a few specimens survive while hundreds died needlessly. Studying toxic animals, breeding endangered species for zoos and release programs, designing release programs and captive colonies is what I do, and sometimes you gotta break a couple eggs to make that omelette and understand all the variables.

Sorry if I offended you in any way.

[Rae]

Why would you continue to "experiment" and kill off more snakes when you saw the results of the first round? I'm not a expert in reptiles and amphibians, and I agree that it is odd you would post this on a forum where frogs are beloved pets, but just coming from a rational, common sense standpoint, why would you want to kill more snakes in such a traumatic way?

Glad to see that I wasnt the only one wondering this ... but I had no idea that Grey tree frogs could be poisonous.

[SkeletalFrog]

Knowledge for its own sake is generally worth it. Pretty much all modern medicine and technology can be traced back to "I wonder what happens if I do this?" For all we know, these could be a parallel system to the Brodie's garter snakes, which have already increasing not just our understanding of evolution and ecology, but also yielded novel insights about sodium channels in neurons, which in turn has countless medical applications.

Opisthoglyph, personally, I'd actually hang on to those metamorphs, with the goal of breeding them and actually setting up an experiment with proper design and enough statistical power to quite possibly be publishable. Maybe get several dozen ribbon snake litters next year, and randomly assort them into groups that are fed the offspring of these metamorphs, some wild-caught tadpoles you gather next year (both greys and other species for an additional control), and some wild-caught tadpoles from a different location many states away. I'd also freeze some tadpoles for chemical assays (I suspect the author of the poster I linked to would be keen on doing some of the chemistry on such a potent toxin).

The number required is tricky, but with some clever stats could probably be reduced. Unfortunately, this is a perfect case for non-parametric statistics, which I'm not particularly familiar with.

Still, I'd save those metamorphs, as their offspring could be a key to determining whether these are inherent toxins like toads or acquired through dietary sources like dart frogs.