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Releasing Chinese giant salamanders back into the wild sounds like a good idea, but it's causing problems for the salamanders and for our understanding of what a species even is.

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I'd like to think that we have some of the basic things in biology figured out by now, like plants need sunlight to grow, and the mitochondria is the powerhouse of the cell, and what a species is. So for that last one, yeah, we don't really know. We have a couple of different definitions that we can use, but in real life, none of them work perfectly.

And while this might seem like a purely academic problem, it is not, because if a thing we thought was one species is actually five different species, then there are a lot fewer purebred Chinese giant salamanders left in the world than we thought. And that is bad news.

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The hellbender, the Japanese giant salamander, and the Chinese giant salamander are all part of the same family and are among the largest living amphibians. The Chinese giant salamander can grow to be around two meters long. That's how long I am. This family has a fossil record that stretches back tens of millions of years into the Mesozoic era, and they seem to have first appeared in Asia, though today the hellbender is only found in the eastern and central US. I've seen one before; they're super cool.

And while they make look soft and slimy, these animals are apex predators in their ecosystems. They eat fish, frogs, crayfish, insects, and sometimes members of their own species, and none of these species of giant salamander are doing well. Populations of both the Japanese giant salamander and the hellbender are declining due to things like habitat loss and water pollution.

But of all of these, the Chinese giant salamander is the worst off. It's been hunted for food extensively since the 1970s, and when it became harder to find them in the wild, people started to farm them, and this really took off in 2004, which seems like maybe it would be a good thing. Like, if they are bred and raised in captivity, people shouldn't need to catch the wild individuals.

But wild salamanders were still being caught, and most of the farmed salamanders actually ended up being sold to start new farms rather than ending up on a dinner table. Salamander farming started to become a pyramid scheme, with even very small salamanders being sold for high prices, and that kept driving up the price of all of the salamanders, giving people an incentive to collect more from the wild.

Now, to combat the decline of the wild salamanders, the Chinese government actually pays farmers to release some of their animals back into the wild as a conservation measure. And while releasing a bunch of these farm salamanders might sound like a good idea, it's causing problems both for the salamanders and for our understanding of what a species is.

In 2018, researchers published a paper on the genetics of the Chinese giant salamander based on tissue samples from both wild-caught and farm-raised individuals taken over the past decade. They found that the DNA of the wild individuals grouped into five distinct clusters, each one associated with a different river drainage area, and these genetic clusters split from each other between about 4.7 and 10.2 million years ago. The farmed salamanders pointed to three more possible species.

So the researchers think there may have been at least eight different species of Chinese giant salamander in the past. The thing is, though, there is no real agreement about how genetically different two animals have to be from each other for them to be considered separate species. For the salamanders, one of the researchers said that they were as genetically different from each other as two other closely related amphibians that we recognize as different species, but that's not the only way we can define a species.

Another definition that gets used pretty often is the biological species concept. It says that two animals are the same species if they can or do interbreed in nature and they can produce fertile offspring, which means we are about to have a problem, because it looks like these different giant salamander species can interbreed. Remember, most of the salamanders that are farmed aren't sold to restaurants; they're sold to other farms.

This means that the farms created a setting that brought together a bunch of salamanders that we know are pretty genetically distinct, and they started to interbreed. And then, a lot of those offspring were released into the wild, so now we either have salamanders living in environments that might not be the ones that their species adapted to, so they may not survive, or they might thrive there and drive the local giant salamander species to extinction, either through competition or by making the gene pool there more homogeneous.

And that brings us back to the species problem, because if they are hybridizing, how are they different species? And that's the whole fundamental question. Biological species concept says interbreeding has to be possible in nature, and there are plenty of reasons why species that can actually interbreed just wouldn't meet up in nature. These include physical barriers, like mountains or rivers that an animal can't cross, and thing like the two species having different behaviors that keep them apart, one being nocturnal and one being diurnal.

And we call them different species, because, functionally, they're reproductively isolated, separate gene pools. Usually. Until we started removing the barriers that kept them apart. Along with moving the Chinese giant salamander around within China, they've also been introduced in Japan, where they can hybridize with the Japanese giant salamander, and we definitely thought those were two different species.

As humans, we need ways to make sense of and talk about the world around us, and the idea of a species is a tool that we use to do that, and how we use that tool can be different depending on what we're trying to do. If we're trying to save a species like the Chinese giant salamander from extinction, we have to be able to say how many of them are left, and if every river system has its own species, each of those is even rarer than we thought, which might mean that they need their own special protections and funding for conservation.

But if there aren't enough individuals of each of those potential species still around to sustain a population, then it might make sense to think of the Chinese giant salamander as a single biological species, one with enough members to be worth trying to save. And like every tool, the idea of a biological species has its strengths and weaknesses. Because biology is messy, our understanding of the world grows and changes over time, and life, uh, finds a way.

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