How the curious life of a newt could ignite a pandemic

  • The eastern U.S. is the world’s salamander hotspot, with more species per area than anywhere else on the planet. Often superabundant, salamanders hold important ecological roles in their habitats.
  • Eastern newts (Notophthalmus viridescens) are the second most widely distributed salamander species in the U.S. They’re also incredibly mobile and are able to transition to a toxic, terrestrial form to move between ponds.
  • Like many other U.S. salamander species, eastern newts are highly susceptible to a fungal pathogen called Bactrachochytrium salamandrivorans (Bsal). While Bsal has yet to make an appearance in North America, it has wreaked havoc on salamander populations in Europe, and biologists worry its impact in the U.S. will be even worse.
  • Their susceptibility to Bsal coupled with their mobility mean eastern newts could act as “super-spreaders” of Bsal if the fungus gets to North America. Researchers worry that not only would the newts themselves face massive die-offs, but also they could quickly spread the disease to other salamander species.

If you take a stroll in the woods, it’s worth pausing for a moment to take in the sights and sounds, peer into the undergrowth, or even turn over a damp log or two. You’ll see birds rummaging for tasty snacks, squirrels scolding you from nearby tree branches, and colorful fungi springing up from the forest floor. And, if you happen to live in the United States and look a little more closely under logs or in ponds, chances are good that you’ll see a salamander or two … or 200.

People tend to think of lush, vibrant tropical forests as the globe’s biodiversity hotspots, and if you’re looking for frogs, by all means, head to the Amazon. But if salamanders are what you’re after, a better bet would be North Carolina. Salamanders are unique among amphibians for preferring the temperate forests of the eastern U.S. to anywhere else on Earth. The U.S. contains both the highest total number of salamander species of any country — at nearly 200 — and the highest species richness, peaking in parts of the Appalachian Mountains. Many of them are found nowhere else in the world.

And the U.S. doesn’t just boast a record abundance of species; in ponds where salamanders are present, their sheer numbers can be staggering. “One pond where we were doing mark and recapture, we caught more than 3,000 individuals over the course of two days,” said Evan Grant, the principal investigator of the U.S. Geological Survey’s Amphibian Research and Monitoring Initiative. “So, the total population of that single pond was maybe 10,000 individuals.”

Those kinds of numbers aren’t atypical. Since salamanders are abundant gape-limited predators (the only limit to what they eat is what will fit in their mouth), they are often at the top of the food chain in the ponds they inhabit, helping to control biodiversity. “There’s no doubt that amphibians are important components of the ecosystem and the food web,” Grant said.

A life in several acts

In the eastern half of the U.S., there is one salamander that stands out from all the rest: the eastern newt (Notophthalmus viridescens). Eastern newts are the second most widely distributed salamander species in the U.S., with a range that spans the entire eastern coast of the country up into Canada, and as far west as Texas and Minnesota. They are split into four subspecies: the red-spotted newt (N. v. viridescens), broken-striped newt (N. v. dorsalis), central newt (N. v. louisianensis) and peninsula newt (N. v. piaropicola).

Juvenile eastern newt “efts” are toxic and bright orange. Image courtesy of Virginia State Parks (CC BY 2.0).

“Eastern newts are a very charismatic species,” said Ana Longo, an amphibian disease ecologist at the University of Florida. “Most people that like to go outdoors, especially in the northeastern U.S., can recognize the species because the eft stage is bright orange.”

To clarify, “newt” is the word commonly used for salamanders in the family Pleurodelinae. So all newts — including the eastern newt — are salamanders, but not all salamanders are newts. While there is no other hard and fast distinction between newts and salamanders, most salamanders referred to as “newt” share the same bizarre life cycle consisting of three morphologically distinct stages, including the fully terrestrial “eft.”

First there is the larval stage, akin to the tadpole stage in frogs. Larval eastern newts are under a centimeter (0.4 inches) long when they hatch, and are fully aquatic, breathing through external gills. The larval stage lasts for between two and five months, after which the young newts undergo their first metamorphosis and transition to their juvenile “eft” stage.

Larval eastern newts are tiny and breathe through external gills. Image by USGS (Public Domain), via Wikimedia Commons.

The eft phase is essentially the newt version of the rebellious teen years. The juvenile newt develops rough skin, swaps its gills for lungs, and sets off on its own into the forest. It also transitions from a dull yellowish-green to bright neon orange accented with vivid red spots. This ostentatious hue isn’t a fashion statement — it warns predators that efts don’t make a very tasty snack. Any predator that tries its luck will get a mouthful of tetrodotoxin (TTX), a powerful neurotoxin that will keep them from coming back for seconds.

This means efts can trundle along right out in the open. Most things in the forest steer clear, although raccoons have been known to decapitate them, flip them over, and flay them to get to the non-toxic flesh under the skin. The eft stage can last anywhere from two to seven years, during which efts will wander far from their original pond. This toxic wandering stage is one of the keys to eastern newts’ impressive range.

The other key? Eastern newts’ three-stage shape-shifting routine isn’t set in stone. If conditions on land aren’t up to snuff, for instance, the newts will skip the eft stage entirely, transitioning straight from a larva to a “neotenic” adult (an adult that retains some larval characteristics).

Or, if a wandering eft selects a pond and metamorphoses into its third stage as an aquatic adult, then finds that the pond isn’t up to snuff, it can transition into a fourth stage: a terrestrial adult. This can occur if the pond is too crowded, doesn’t have enough food, or has too many parasites. Such flexibility means that eastern newts are great at colonizing new areas and adapting to changing habitat conditions.

“Eastern newts are really cool in their life history in that they can inhabit temporary wetlands and more permanent wetlands because they have this ability to move between the aquatic and terrestrial phase,” Grant said.

This story first appeared on Mongabay

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