Leaving society after a long isolation becomes embarrassing. Ask the Pahrump poolfish, solitary in a desert for some 10,000 years.
This fish to hold in the hand (Empetrichthys latos) has a chubby torpedo shape and an almost smiling mouth. Until the 1950s, this species had three forms, each evolving in its own spring. Today, only one survives, which grew in a spring-fed oasis in the Pahrump Valley of the Mojave Desert, about an hour’s drive west of Las Vegas.
Fish in a desert aren’t that weird when we look at the long term (SN: 01/26/16). In a past life, some desert valleys were ancient lakes. As the lakes in the area dried up, the fish got stuck in the remaining puddles. Over time, various stranded species adapted to the whims of their private microlakes, and a desert fish version of the various Galapagos Island finches emerged.
“We like to say that Darwin, had he had a different travel agent, might 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. latos evolved was Manse Spring on a private ranch. From a distance, the spring looked “like a small clump of trees,” recalls ecologist Shawn Goodchild, who is now based in Lake Park, Minnesota. The patch of desert greenery surrounded the entire natural range of the Pahrump poolfish, running the length of an Olympic swimming pool.
In the 1960s, biologists feared the fish were doomed. The flow from the spring had dropped by about 70% as irrigation from desert farms sucked up the water. And disastrous predators arrived: a child’s abandoned goldfish. Conservation officials fought back, but neither poison nor dynamite wiped out the new arrivals. And then in August 1975, Manse Spring dried up.
Conservation officials had moved some poolfish to other sources, but the long-isolated species just didn’t seem to have the dangers of living with other types of fish. The poolfish were easily caught by predators in their new home.
Lab tests of fake fish murder scenes may help explain why. For example, researchers contaminated the water of an aquarium with pieces of mashed fish. In an expected reaction, the fathead minnows (Pimephales promelas) panicked at the sight of tracks of dead minnows drifting in the water and huddled low in the tank. Pahrump’s pool fish in water contaminated with blender whipped skin of their kind kept swimming around the upper waters as if the smell of corpses was no scarier than tap water. Literally. Stockwell and his colleagues can tell this because they performed a fear test with non-frightening dechlorinated tap water. Poolfish didn’t snuggle then eitherreports the team in the August 31 Proceedings of the Royal Society B.
Then, however, Stockwell and a colleague were pondering rescued pool fish from livestock tanks when nearby dragonflies caught the attention of researchers.
Before dragonflies become shimmering aerial marvels, young ones prowl underwater as violent predators. In moves worthy of creepy aliens in a sci-fi movie, many dragonfly nymphs can stick their jaws out of their heads to scoop up prey, including fish eggs and fish larvae. With young dragonflies prowling the bottom of a pond and plants, pond fish moving up the water column “would be a good way to reduce their risk,” Stockwell says. The testing of this idea has begun.
Fish that people thought foolishly naive may just be advised in a different way. Especially after isolation in a desert with dragons.