Maybe you gave your last realtor a long series of must-haves: a washing machine in unit, proximity to the train, a gas stovetop. But there's no way you're as picky as the driftwood hopper. This minute crustacean will only live in rotting chunks of driftwood. David Wildish, a marine zoologist at Fisheries and Oceans Canada, is one of very few scientists who study tiny animals called talitrids. These crustaceans include sand hoppers (also known as sand fleas) along with ocean-living species. Within this family, the driftwood hoppers are simultaneously homebodies and world travelers. "They feed there and breed there" inside decaying driftwood logs, Wildish says. Tucked in their homes, driftwood hoppers are safe from the shorebirds that prey on ordinary sand hoppers. Females store their fertilized eggs inside a body pouch until they hatch, like a less charming kangaroo. Sometimes, driftwood hoppers "also get a free ride to a new location," Wildish says. "Driftwood logs can float and, if currents and wind are right, can be transported to oceanic islands distant from continents." This may help explain how sand hoppers and other kinds of talitrids have ended up on land masses around the world. Perhaps as they washed ashore on rotting tree pieces, driftwood hoppers crept out to explore, later evolving into the species that now inhabit beaches, forests, and caves. In a new paper, Wildish describes two newly discovered species of driftwood hopper. One was collected from the shores of the Mediterranean in Italy. The other came from a single rotting log of Douglas fir that washed up in England. This species is the most interesting, Wildish says, and is so different from other driftwood hoppers that he believes it's a new genus. Unlike its known relatives, this hopper stays small and keeps its juvenile appearance for its whole life (a trait biologists call "neoteny"). Not that any of the driftwood hoppers are big. All of them are under 1.5 centimeters long, Wildish says. Figuring out why they need to stay so small is just one of the questions he's working to answer. "The dispersal and evolution of talitrids is a fascinating and nearly unexplored field," Wildish says. He guesses that 80 to 90 percent of talitrid species are still waiting to be discovered. The hoppers that are confined to driftwood are especially mysterious. And they're fragile: a whole local population can be wiped out when a log dries up on a beach, or is collected for firewood, or sinks into the ocean. Wildish is hoping to solve evolutionary puzzles by studying these elusive animals—even if he doesn't have much company, he says. "Few people carry an axe to open driftwood logs stranded on the shore."
Images: top by Tom Gill (via Flickr); bottom by Dr. David Wildish.
Wildish, D. (2014). New genus and two new species of driftwood hoppers (Crustacea, Amphipoda, Talitridae) from northeast Atlantic and Mediterranean coastal regions Zoosystematics and Evolution, 90 (2), 133-146 DOI: 10.3897/zse.90.8410