Journal Article Review: Tetrodotoxin does not protect red-spotted newts, Notophthalmus viridescens, from intestinal parasites

Toxicon

Volume 60, Issue 1, July 2012, Pages 66–69

Tetrodotoxin does not protect red-spotted newts, Notophthalmus viridescens, from intestinal parasites. 

Dietrich Mebs, Mari Yotsu-Yamashita, Hanns Martin Seitz, Osamu Arakawa

We have seen this little guy a couple times throughout our semester on our lab quizzes and exam. I even had to give a power point presentation for our lab final on how to be able to identify this herp from others. One of the most interesting things I found while preparing that presentation was on page 442 of our Reptiles and Amphibians Peterson Field Guide. The field guide said that these newts have skin gland secretions that will scare away predators after they have bitten them and tasted how bitter they are. We had also just covered how the Aposematic coloration in poisonous frogs serves as an indicator of "Hey I'm not good for your health so you better not eat me." The brightly colored spots on Notophthalmus viridescens seem to also have that same effect with the bitter skin secretions.

But are there some predators that can get past the skin secretions and still hurt these little guys? Turns out the answer is yes and they are very minuscule attackers. More precisely put, they are parasites. In the journal article "Tetrodotoxin does not protect red-spotted newts, Notophthalmus viridescens, from intestinal parasites," the bitter skin secretions finally have a scientific name: Tetrodotoxin or TTX for short and it's analogue 6-epiTTX. 

The researchers in this article collected a sample size of 30 adult Red Spotted Newts from a research center in Pennsylvania and froze them :(sad I know) to quickly kill them. They then dissected the intestines of these newts to see which and how many were infected with parasites. Running a lot of extensive Histological and Immunohistological analysis, they found the three main parasites infesting these newts were Nematodes, Trematodes and Cestodes.

"Fig. 1. Intestinal parasites of the red-spotted newt, Notophthalmus viridescens. (A, B) Nematodes belonging to the order

Trichurida, probably of the genus Capillaria, which typically live inside tissues, not in the intestinal lumen; in (B) with a prominent stichosome. (C) Cestode (larval stage?) (D) Trematode (operculated eggs). Trichrome staining. (Mebs, D., et al, 2012)"  Figure taken from: Tetrodotoxin does not protect red-spotted newts, Notophthalmus viridescens, from intestinal parasites. 

As you can see from the picture of the intestines and skins of these newts, the Nematodes and Trematodes have taken over and are using these newts as hosts to procreate and mature. These two parasites were found in the tissues as well as the intestines but the Cestodes were found only in the intestines of the newts.

The researchers found that these parasites also contain high levels of TTX just like the Red Spotted Newts which concludes that the newts cannot protect themselves from parasites with use of their TTX toxins. They also ran a quantitative analysis on the newts and found that some of the newts and parasites did not have TTX and instead had the analogue 6-epiTTX. Not quite sure what the analogue means but I am assuming it means if they somehow have not produced TTX, they can still produce an alternative toxin that is extremely similar in effect.

Notophthalmus viridescens lives in ponds and wetland areas when they have not evolved into the land Eft stage. Another parasite that was found to attack the newts in this wet habitat were leeches. This is even more interesting to see since leeches do not attack their hosts from the inside like the other parasites in this study do. They instead latch onto the outside and deplete their host's nutrients in that manner. Given the newts secrete TTX on their skin, one would think the leeches would not stay attached to the newts, but they do. This is because the leeches also contain TTX and the newts were observed to come out of the water trying to bite the leeches off of them. If they couldn't get them off, they ended up dying.

This article study shows us how the TTX secretions is effective in making sure other animals do not ingest an infected N. viridescens. Being ingested while infected would increase the parasite's ability to have more hosts. Fortunately, the infestation will stop with the newts. This does not mean other animals cannot obtain parasites. It simply means an animal will not become infected with parasites from a N. viridescens because the TTX secreted from the newt is completely effective in stopping predators from ingesting them. Sadly, the TTX and it's analogue 6-epiTTX does not stop parasites from infecting the newts.

This was an interesting article to read and if you would like to read it for yourself, click here. You will most definitely need to enter your Cougar ID to get access to this journal article so make sure you have that handy. 

Works Cited:

Conant, R., & Collins, J. T. (1998). A field guide to reptiles & amphibians: eastern and central North America (3rd ed.). Boston: Houghton Mifflin.

Mebs, D., Yotsu-Yamashita, M., Seitz, H. M., & Arakawa, O. (2012). Tetrodotoxin does not protect red-spotted newts, Notophthalmus viridescens, from intestinal parasites. Toxicon, 60(1), 66-69.