It can be hard to make it into society after long periods of isolation. Ask the Pahrump Poolfish, lonely people who have lived in a desert for over 10,000 years.
This hold-in-your-hand-size fish (Empetrichthys latos) has a chubby, torpedo shape and a mouth that looks as if it’s almost smiling. This species was composed of three different forms that each evolved in its own spring until the 1950s. Now only one survives, which developed in a spring-fed oasis in the Mojave Desert’s Pahrump Valley, about an hour’s drive west of Las Vegas.
Fishes in a desert don’t seem so bizarreWhen you look at the long-term (SN: 1/26/16). Some desert valleys used to be ancient lakes in a previous life. As the region’s lakes dried up, fish got stuck in the remaining puddles. Various stranded species over time adapted to quirks of their private microlakes, and a desert-fish version of the Galapagos Islands’ diverse finches arose.
“We like to say that Darwin, if he had a different travel agent, could have come to the same conclusions just from the desert,” says evolutionary biologist Craig Stockwell of North Dakota State University in Fargo.
The desert “island” where E. latosManse Spring was created on a private ranch. From a distance, the spring looked “just like a little clump of trees,” remembers ecologist Shawn Goodchild, who is now based in Lake Park, Minn. The spot of desert greenery surrounded the Pahrump poolfish’s entire native range, about the length of an Olympic swimming pool.
In the 1960s, biologists were worried that fish would die. The spring’s flow rate had dropped some 70 percent as irrigation for farms in the desert sucked away water. And disastrous predators arrived: a kid’s discarded goldfish. Conservation managers fought back, but they could not eradicate the newcomers with poison or dynamite. Manse Spring finally dried up in August 1975.
Conservation managers had moved some poolfish to other springs, but the long-isolated species just didn’t seem to get the dangers of living with other kinds of fishes. Predators easily took the poolfish from their new home.
It is possible that lab tests of fish-murder scenes could help to explain this. For example, researchers added fish bits to aquarium water. Fathead minnows () were the expected result.Pimephales promelasThe fish were alarmed at the traces of dead minnows in the water, and they huddled down low in the tank. The Pahrump poolfish, swimming in water tainted by blender-whizzed skin from their species, just kept swimming around the water’s upper parts as if it were not more dangerous than tap water. Literally. Stockwell and coworkers can affirm that because they did a fear testing with non-scary, dechlorinated tapwater. Poolfish didn’t huddle then eitherThe team reports to the Aug. 31 Proceedings of the Royal Society B.
Then, however, Stockwell and a colleague were musing about some rescued poolfish in cattle tanks when nearby dragonflies caught the researchers’ attention.
The young dragonflies, before they become magnificent aerial beautys, are violent predators underwater. Many dragonfly Nymphs can fire their jaws out of their heads to capture prey. This is reminiscent of aliens in sci-fi movies. With young dragonflies prowling a pool’s bottom and plants, poolfish moving up the water column “would be a good way to reduce their risk,” Stockwell says. The idea is being tested.
Fish that people thought were foolishly naïve may just be savvy in a different way. Particularly after being isolated in a desert filled with dragons.
