Moss sex driven by scent

During mating season, a moss needs a little help from its friends — and it uses smell to recruit them. A new study has found that mosses, which were long thought to require only water or wind to reproduce, release an aroma that entices tiny animals such as mites and little bugs called springtails to help fertilize the plants. The discovery challenges current ideas about plant evolution, but experts say it raises more questions than it answers.

For mosses, sex can be tricky. They can reproduce asexually, or they can develop male and female sex organs and wait for their fragile sperm to travel from one to the other. If the latter occurs, they rely on the elements — wind or splashing rain — to help with transport.

In 2006, researchers discovered a third means of delivery. They found that tiny arthropods, a group of creepy-crawlies that includes mites and springtails, seemed to help disperse moss sperm. But the study didn’t pinpoint how they did it or whether this kind of fertilization was critical to the moss life cycle.

In hopes of answering those lingering questions, biologist Sarah Eppley of Portland State University in Oregon and colleagues gathered and grew moss samples from local forests and tested reproductive outcomes with and without rain and springtails. They found that water alone and springtails alone were equally effective at fertilizing mosses, but putting the two together made the mosses more than twice as successful at reproducing.

With arthropods’ key role confirmed, the team turned to how fertilization happens. They wondered if chemical signals or scents are involved as they are for flowering plants. So they isolated the springtails into chambers where the critters couldn’t feel or detect the moss itself but could smell the moss scent as it wafted toward them. The springtails went wild nevertheless, clamoring to reach the scent’s source, especially when the moss plant was a female. The scent attracts the arthropods just as a flower’s aroma draws pollinators that help it reproduce, the researchers report online Wednesday in Nature.

Because mosses are considered the closest relatives of Earth’s earliest land plants, the findings could broaden scientists’ ideas about how plant life arose and evolved. The results suggest that arthropods, which have influenced everything from color to timing of the life cycle in flowering plants, may have shaped plant evolution well before the origin of flowers. “There’s this much more complicated system than we knew, and that will expand ideas about how plants evolved,” says Eppley.

“This is an exciting, lovely study,” says Robert Raguso, a chemical ecologist at Cornell University, who works on mosses but was not involved in the research. “This really shows that mosses and arthropods aren’t just bumping into each other in the dark. ... They’re all talking to each other.”

Still, a number of mysteries remain, he says. “This generates questions like what are the little buggers getting out of this arrangement? Are the mosses feeding them? Are they springtail singles’ bars, where springtails hook up and mate? That should be the next study.”

Another unanswered question is what this seductive scent actually smells like. The team’s chemical analysis hasn’t yet identified the specific compounds that lure the arthropods or linked them to more familiar floral smells. “Springtails like rotting leaves and decay,” Eppley notes, “so the smell might not be something we’re going to make perfume out of anytime soon.”