Devil and the deep pupfish

Ambika Kamath | Updated on February 23, 2018 Published on February 23, 2018

Biological treasure: Biologists may never figure out how the historic pupfish ever got to Devils Hole   -  Image courtesy: USFWS image library

A rocky desert pothole in Southwestern US is home to a historic breed of pupfish that has triggered biological theories on how they managed to survive over several hundred years

It’s not often that I first learn about a species of animal from someone who studies history. But the Devils Hole pupfish is an especially curious animal, and Kevin Brown, who has been tracing the story of its interactions with humans and our politics, is an environmental historian. And to him, the Devils Hole pupfish is a compelling example of the multitude of ways in which humans and nature are deeply interconnected.

The story of this tiny fish species, which is found in just a single little water body in the Southwestern US and whose every individual could together fit in a small bucket, is “not just about biology or about ecology but also about human history.”

Devils Hole is not, in and of itself, an arresting sight. A mere 10 feet by 60 feet at its surface and surrounded by steep rocks, you’d be forgiven for not paying much attention to this geothermal pool if you happened upon it. At his first encounter with the water body, Brown was partly underwhelmed. “It’s on the side of a dirt road in the middle of the desert, and you…just look down into this little pot of water and you go ‘Hm. Okay’.” Absent of any sense of Devils Hole’s inhabitants, “it seems just like another desert pothole,” Brown said. But on the other hand, “you can stand at the foot of this pool, and at one time, with your own eyes, see 90 per cent of an entire species.”

Investigate a little further, and you’ll quickly see that this ecosystem has hidden depths. In the case of Devils Hole itself, this is quite literally true — no one knows exactly how deep this pool extends, for divers have never reached the bottom and survived to tell the tale. But the same is true, more metaphorically, of the Devils Hole pupfish as well, for it raises the question of what we actually mean when we talk of conserving nature.

For the longest time, Devils Hole and its pupfish were not officially protected by the National Parks Service, which saw its mission as being, as Brown put it, “to protect mostly scenic wonders for people to enjoy, as opposed to biodiversity in and of itself.” With time, though, this mission evolved. An important step along this path was their inclusion on the very first official list of endangered species in the US. Recalling this history reminds us, Brown argued, that “an endangered species is not a category of being,” as we biologists are wont to consider it; rather, “it’s a legal and political description.”

But describing a species as endangered undoubtedly goes on to shape the attention that biologists direct at it. Understanding whether a species’ future is at risk depends, in many ways, on understanding its past. And in attempting such an understanding, biologists studying the Devils Hole pupfish quickly ran into a simple question — when did pupfish get to Devils Hole?

This turns out to be a controversial issue — different scientists using different methods estimate that pupfish entered Devils Hole either 60,000 years ago, raising the question of how this tiny population has managed to survive so long, or a mere 200 years ago, provoking us to wonder how these fish made the leap across the desert.

Like historians, evolutionary biologists work with what’s written, except that for living creatures, the relevant information is written in DNA. Unlike records written by humans, however, DNA never comes with a date scribbled on it. Thus, evolutionary biologists must devise mathematical models to use information contained in DNA to deduce how old species are. All mathematical models make assumptions, however, and because nature is usually messier than maths, actual data almost never fulfil these assumptions. For example, when calculating how long ago two species became distinct from one another based on differences between their DNA, it matters a huge deal how quickly DNA changes or “mutates.”

But measuring DNA mutation rates is difficult, and knowing how these rates change with time is nearly impossible, so evolutionary biologists often assume in their mathematical models that these mutation rates stay roughly constant across species and through time. But the weird biology of the Devils Hole pupfish — these fish are tiny, don’t live too long, have wildly varying population sizes from year to year, and are found in an incredibly harsh environment — makes it likely that these and other assumptions of the mathematical models are violated. The upshot is that biologists may simply never know how old this pupfish is, or how it got to Devils Hole.

The idea that the Devils Hole pupfish may be only 200 years old raises an intriguing possibility, one that could be confirmed by historical research or perhaps an amalgamation of historical and biological approaches. “It’s plausible that people put them in there, either intentionally or accidentally,” Brown suggested, “maybe humans played a role in creating this species.”

To a biologist, such an origin intertwined with human history might make the species less deserving of protection — indeed biologists have wondered if conservation measures “are warranted for a species which might simply be a recent anthropogenic artefact.” But Brown disagrees saying, “In some ways it makes them more interesting, because they’re then both a natural and a cultural resource.”

Ambika Kamath

Ambika Kamath is a behavioural ecologist, currently based at the University of California, Santa Barbara; ambikamath@gmail.com

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Published on February 23, 2018
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