Devils Hole Pupfish
Even though I've mostly withdrawn from Facebook, I still very much appreciate many of the posts that appear from following BBC Earth. One that I enjoyed recently was a report on the Devils Hole Pupfish. This species lives exclusively in the Mojave Desert, a region that receives around 13 cm (5") of rain per year. Every individual of the species that has ever lived is believed to have existed in one single water feature, a modest geothermal pool called Devils Hole.
As an aside, Devils Hole itself is quite a remarkable feature. Thanks to its connection to a vast aquifer, the water at its surface will slosh around visibly in response to earthquakes as far away as Indonesia.
The fish is what I'd like to focus on though. They're fairly modest critters. I don't think grey-blue and blobbish would be an unfair assessment. And yet these fish are fascinating because they have made it to this small isolated pool and survived there.
What brought them back into the public eye most recently was a discovery that seems to confirm, and consequently deepen, the mystery of how they got there. A genetic analysis suggests the the species has existed for approximately 50,000 to 80,000 years, which aligns with the age of Devils Hole. This goes against the less glamorous theories that the fish may have been introduced relatively recently by Native Americans.
As usual, the information in the BBC article is a bit editorialized and makes it seem like these are the only fish for hundreds of miles, but in fact there are several closely related species of pupfish in the same general region. The main difference is that those other pupfish are not confined to a single pool, and their distribution is more easily explained by geological history (glacial lakes that have dried up to form scattered pools). On the other hand, Devils Hole is believed to have only ever been connected to other water bodies by aquifer, and fish typically don't traverse aquifers.
I think if you focus on the 'how did they get there' part you miss out on something even more fascinating. These fish have survived in this little pool, and seemingly for enough years to speciate. With such severe limits on population size and an origin that likely involves a small number of individuals, you would think the lack of genetic diversity would cause a collapse. Or you would expect that at some point a catastrophic event would wipe them out, especially if they have been there over a long enough time-frame for the regional climate to change.
I'm not convinced that the story of this species origin is any more riveting than some eggs riding in on the leg of a bird, and I'm not convinced that they've been there for 50,000 years, but I am convinced that their presence is an astounding testament to the resilience and ubiquity of nature.