One of the most inbred animals in the world lives in Death Valley

Death Valley derives its fame from the extremes. The 3.3 million acre park is one of the hottest and driest places in the world. Yet the park is not so one-dimensional – it has a lot more depth than you might think.

A vast network of aquatic systems meanders beneath the surface of Death Valley, taking the form of a maze of caverns and subterranean lakes. When rain or snowmelt seeps into the ground, the water enters an aquifer and eventually collects in the underground waterway. The process is slow. It takes about 10,000 years for a single water molecule to reach these caverns from the surface, according to the National Park Service.

The entrance to this abyss is called Devils Hole, and the name corresponds to the place. Go to this part of Death Valley and you’ll come across a hole in the Earth with water hot enough for the Devil himself. The narrow passage drops into cavernous, seemingly inaccessible depths. Divers have explored as low as 500 feet below the surface, and they still haven’t touched bottom.

A tiny underwater world

Despite its great depths, many biologists focus their attention on the top 80 feet of Devils Hole, where there is a compact shelf of shallower water. Here, the Devils Hole pupfish (Cyprinodon diabolis) makes his home. Its size of 10 by 20 feet (3 by 6 meters) gives it the smallest known range of any vertebrate species.

In addition to the cramped quarters, this part of Devils Hole presents other challenges for aquatic organisms. It maintains an almost constant temperature of 34°C (93°F) and receives no direct sunlight during the winter (limiting the growth of algae, which the pupfish eat). For most fish, living in a black hot tub would already be intolerable. Add to that the low concentration of dissolved oxygen, which would be lethal to many underwater organisms, and you’ll see why the Devils Hole pupfish doesn’t have to worry about anyone else coming.

In fact, you won’t find the Devils Hole pupfish anywhere else. The 30 known species of pupfish, so named for their playful puppy-like movements, share a general ability to withstand harsh living conditions. But even among this hardy group, the Devils Hole pupfish takes the extreme lifestyle to a new level. Their mere existence amounts to a miracle. In 2013, their number dropped to just 35 individuals. Today, the number of Devils Hole pupfish individuals hovers around 263, the highest population recorded in 19 years.

There are many reasons why this pupfish can be doomed: climate change, habitat decline, falling water levels, and human activity all threaten this isolated population. But we were never really convinced that the Devils Hole pupfish would stick around. Scientists and policy makers chose to classify the species as endangered in 1967, almost immediately after the Endangered Species Act – at the time called the Species Preservation Act – came into effect. endangered.

Many sympathize with the pupfish as an underdog who was expected to lose but kept fighting. You might even have heard about it on the famous podcast Criminal, which documented the public outcry that resulted when a few people unwittingly partied a little too loud near Devils Hole. People really care about these fish.

A shallow gene pool

Now, new research has identified another obstacle to their survival: incest.

Devils Hole’s isolation makes it difficult to find a new companion. It’s a bit like constantly bumping into your ex at the store, if your ex was also your cousin. Earlier this month, scientists reported results in Proceedings of the Royal Society from a genetic analysis performed on the Devils Hole pupfish. The researchers found that the species’ sequences are 58% identical on average, which is equivalent to “five to six generations of sibling matings”, according to Christopher Martin, an evolutionary biologist at the University of California. at Berkeley, and co-author of the paper. Researchers believe that the Devils Hole Pupfish is the most inbred species in the world.

In this study, the researchers sequenced the entire genome of eight Devils Hole Pupfish and one preserved specimen from the 1980s. They also sequenced the genomes of related species in surrounding areas.

Specimens from the 1980s helped researchers determine that the population was highly inbred even before the population bottlenecks in 2013 and 2017. This finding suggests that the pupfish has a history of repeated population contractions. Not surprisingly, Devils Hole pupfish harbor a significantly higher mutational load than all other desert pupfish in the study.

Pupfish Mutations

Researchers have discovered serious deleterious genetic mutations. For example, all eight specimens had mutations in a gene associated with sperm morphology. This makes it surprising that the fish can reproduce. They also found five genetic deletions associated with hypoxia, or low oxygen conditions. The changes in these genes are not surprising, given that Devils Hole is a highly hypoxic environment.

Paradoxically, however, the deletions suggest that the Devils Hole pupfish may be ill-equipped to physiologically cope with the stresses of a low-oxygen environment. This could explain why they tend not to breed as well as other pupfish.

The authors warn that it would be foolhardy to start managing these deleterious variants immediately. We must first link these genetic changes to decreases in survival or reproduction.

The study suggests that the Devil’s Hole pupfish remains in serious danger. Climate change will add to the peril by shortening the seasonal period when conditions are optimal for hatching on the shallow shelf where Devils Hole pupfish spawn. Because environmental stress tends to exacerbate problems created by inbreeding, we know that Devils Hole pupfish face interactive threats that make survival more difficult. Like many other threats that are set to wipe out these thumb-sized creatures, it seems the Devils Hole pupfish has taken its genetic situation into account. No one can ignore how their population has continued to grow.

We might even be able to help. Integrating genome sampling into conservation efforts is a new and promising scientific endeavor. Once we have linked a mutation to a change in survival or fertility, we can closely monitor that gene and spot mutations as they occur. This foresight gives scientists a better chance of trying to use captive breeding programs to improve genetic diversity before populations drop beyond recoverable levels.

This is the crux of endangered species management – ​​you have to stop a species from crossing that finish line. There is no turning back once a species has disappeared.