Caecilians: Defense

Summary: Join Kiersten as she talks about how caecilians defend themselves against predators.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean.

 

Show Notes: 

“Morphological Evidence for an Oral Venom System in Caecilian Amphibians,” by Pedro Luis Mailho-Fontana, Marta Maria Antoniazzi, Cesar Alenandre, Daniel Carvalho Pimenta, Juliana Mozer Sciani, Edmund D. Brodie Jr., and Carlos Jared. iScience, Volume 23. Issue 7,101234, July 2020. https://doi.org/10.1016/j.isci.2020.101234

 

“Predation on Caecilians (Caecilia orientalis) by Hawks (Leucopternis princeps) Depends on Rainfall,” by Harold F. Greeney, Rudy A. Gelis, and W. Chris Funk. Herpetological Review, 2008, 39(2), 162-164. 

 

“Skin gland concentrations adapted to different evolutionary pressures in the head and posterior regions of the caecilian Siphonops annulatus,” by Carlos Jared, Pedro Luis Mailho-Fontana, Rafael Marquez-Porto, Juliana Mozer Sciani, Daniel Carvalho Pimenta, Edmund D. Brodie Jr., and Marta Maria Antoniazzi. Scientific Reports 8, Article number: 3576 (2018).

 

“This Worm-Like Amphibian May Pack a Venomous Bite,” by Alex Fox, Smithsonian Magazine, https://www.smithsonianmag.com/smart-news/worm-amphibian-may-pack-venomous-bite-180975266/

Music written and performed by Katherine Camp

 

Transcript

(Piano music plays)

Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

(Piano music stops)

Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

This episode continues caecilians and the eighth thing I like about these amazing amphibians is how they defend themselves.

Who are caecilians protecting themselves from? We’re aware of a few species of animals that eat caecilians. Snakes, spiders, turtles, and ants have all been reported preying on caecilians. In 2008 a surprising animal was added to this list. A group of researchers watching cameras set up to record a Barred hawk nesting site in Ecuador captured something unexpected. The parents fed their single chick many different animals including 50 individual Caecilia orientalis, a terrestrial caecilian species. Researchers are unsure how a hawk was able to find a subterranean animal easily enough to bring 50 of them to their young, but we can add these hawks to the list of caecilian predators.

So how do caecilians protect themselves from getting eaten? The first way caecilians protect themselves from predators is really a bit of a happy accident and that’s their fossorial lifestyle. Spending most of your life underground does cut down on the number of predators that can find you, although it doesn’t seem to be slowing down the Barred Hawk. Even so, evolution has given terrestrial caecilians a bit of a jump start on protecting themselves by equipping them to live underground. Aquatic caecilians spend a large amount of time close to the substrate of their chosen water source and hidden in dense plant matter, also a great place to start protecting themselves.

Caecilians do have a few other tricks up their sleeves to actively defend themselves from predators. 

But before we get to those, I want to tell you that most of the information I’ve found on this subject comes from the study of one species of caecilian, Siphonops annulatus, so it may not apply to all species of caecilians. One more I caveat need to mention is that this information is based on educated inference. Because we have not actively seen caecilians defending themselves from predators, we are making some assumptions based on the natural history of other species of animals.

Now that’s out of the way, let’s get to the really cool stuff!

Most amphibians are covered in mucus to help with oxygen transmission and disease protection, caecilians are no exception. Actually, caecilians have more mucus glands than any other amphibian. If you remember, in the locomotion episode, I mentioned that some fossorial caecilians, such as Siphonops annulatus, use their mucus to help lubricate their tunnels to make movement easier. To do this they have glands on their heads that create and release the mucus. They also have glands on their rear end and scientists assumed it was for the same reason. Not so. The gland on the rear end expels a poisonous mucus. We assume that this poison is excreted to protect them from predators that might follow them into their tunnels. 

They also tend to plug the opening of their tunnels with their rounded bums when they are sleeping or resting. A perfect way to keep a predator at bay, greet them with a face full of poison!  

Another option Siphonops annulatus has is their bite. A recent study from 2020 has shown that Siphonops annulatus may have a venomous bite! Once again this is a first for an amphibian. It’s not the first time toxins have been found in Order Amphibia. The most famous example is poison arrow dart frogs that produce poison that is excreted onto their skin. Now, they are classified as poisonous because the toxin is transferred through touch. Animals classified as venomous such as rattlesnakes and Gila monsters inject their toxin into another animal through something like fangs or teeth. Up until this recent discovery, we thought there were no venomous amphibians. 

The study found glands closely associated with this caecilian’s teeth. They found the glands in both the upper and lower jaws. These glands are the same type of glands found in certain venomous reptiles. Within the glands researchers found a combination of mucus, lipids, and proteins. The researchers isolated the cells found in the glands and discovered a similarity to oral venom glands identified in the Texas alligator lizard. As of the recording of this podcast the Texas Alligator lizard and Siphonops annulatus are not classified as venomous, but we’ll have to wait to see what future research determines.

Unlike snake venom glands there appear to be no muscles related to the glands in Siphonops annulatus to facilitate injection of poison, but the caecilian teeth are covered in mucus produced by these oral glands. This leads the scientists to believe that the venom may be secreted when the caecilian clamps it jaws down tightly on a prey item.

There needs to be more study to determine whether this substance is a toxin used to immobilize prey and if it is truly a venomous substance at all. Another purpose for this adaptation may also be as a defense against predators. Considering we’ve never seen defensive behavior in Siphonops annulatus in situ, these glands might be related to protection against predators. 

These scientists did find oral glands present in other species of terrestrial caecilians meaning that they all may have venom that they use for capturing prey and for defense. Further research needs to be done to confirm or debunk this. When they looked at some aquatic caecilians they found no oral glands, which truly intrigues researchers. 

That is all we currently know about how caecilians protect themselves from predation, but I’m sure future research will turn up even more amazing information, and I can’t wait to read about those discoveries because defense is my eighth favorite thing about caecilians. 

 

I want to take a moment to say hello to a young listener. Lydia, thanks for listening and I’m so glad you’re enjoying the podcast. Speaking of which…

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Join me next week for another thing I like about caecilians!

 

(Piano Music plays) 

This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.