Things are not going well for frogs. A type of fungus known as chytrid has decimated populations around the globe, causing the serious decline or extinction of 200 species. Even worse, scientists believe chytrid is capable of infecting most of the world’s 6,000-some amphibian varieties -- an event that would likely be cataclysmic for food chains worldwide. Luckily, a paper published in the online journal PLOS One this week offers some insight about how chytrid might have first spread -- and perhaps how to stop it.
But I have to warn you: it’s about to get a little weird.
It involves pregnancy tests. Nowadays we’ve got plastic, pastel-colored sticks with plus-signs and smiley faces to tell women when they’re expecting. But in the 1930s, those didn’t exist. Back then, women gave a sample of their urine to a scientist, who then promptly injected it into the hind leg of an African clawed frog (Xenopus laevis). If the woman was truly pregnant, her urine would contain human chorionic gonadotropin, or hCG -- the same hormone detected by modern tests -- which also happens to induce ovulation in frogs. In other words, if the frog started laying eggs the woman was pregnant. I promise, this is a real thing.
As you can imagine, the invention of a reliable pregnancy test was a pretty big hoopla, and the technology spread quickly -- which meant African clawed frogs were now on world tour. Little did we know then, but some of those frogs had chytrid.
Scientists have suspected that African clawed frogs might have been the vector for chytrid for some time now, but this week’s paper seeks to make it official. The authors were able to confirm this hypothesis by testing archived frog samples from 1871 up to 2010, finding that the fungus was indeed present before we started shipping frogs around the world. They also confirmed that the same kind of chytrid is present in feral populations of African clawed frogs in California today. (It seems many research facilities may have set their test frogs loose when less slimy pregnancy tests were invented in the 1960s, allowing the creatures to take up residence in many foreign lands. Though this species is still a lab favorite for outlandish experiments.)
The fact that African clawed frogs were able to transport chytrid around the globe without succumbing to its effects is both bad and good. On the one hand, it allowed an outbreak to burn through amphibian populations (many of them already endangered or struggling) the world over. But on the other hand, unlocking the secrets of how the African clawed frog evolved a resistance to the fungus, allowing them to be carriers who aren’t killed, might be the only hope we have for the amphibians that remain. Scientists have managed to save other species from the fungus in the lab, though a field cure remains elusive.
Perhaps the most important strategy, though, is to keep the worldwide transport and sale of frogs (mainly for pets and laboratory use) under control. At least some companies are starting to check their shipments more closely for chytrid. Others need to hop on it soon.
Image: Holger Krisp