Unique New Worm Species Has Reversed Its Own Evolution

Chuck Bednar for redOrbit.com – Your Universe Online
An unusual, newly discovered type deep-sea worm lives on the bones of dead animals and features males that have grown significantly larger than their predecessors, researchers from the Scripps Institution of Oceanography report in a new study.
According to San Francisco Chronicle science editor David Perlman, the authors of the new Current Biology paper detailing the discovery report that the worms have reversed their own course of evolution like no other creature before. Not only have they grown larger than their forebears, they mate in vastly different ways than their closest relatives.
[ Watch the Video: The Story Of A Bizarre Deep-Sea Bone Worm Takes An Unexpected Twist ]
The worms were initially discovered on the remains of a long-drowned seal at the bottom of Monterey Bay, some 3,000 feet below the surface, by marine biologist Greg Rouse during expeditions above the mile-deep Monterey Canyon and off the Oregon coast. The species, which has been named Osedax priapus, is the second known species of the bone-consuming Osedax worms discovered (the first came in 2002).
Monterey Bay Aquarium Research Institute (MBARI) evolutionary biologist Robert Vrijenhoek, who captained the research vessel used by Rouse during the new discovery, was also responsible for the previous find. At the time, he indicated that the creatures had no mouth, stomach, legs or eyes. However, the body of each of the females held hundreds of males that were so small, they resembled larvae and lived on small bits of the female’s eggs.
Rouse told Perlman that the new worms, which were named in honor of the mythological god of fertility, were an “evolutionary oddity unlike any other in the animal kingdom.” The males are now as large as the females and tens of thousands of times larger than the other species, he explained, and instead of surviving on scraps inside the opposite sex of the species, they were witnessed devouring the same rotting bones as the females.
“This worm was weird enough as it was and now it’s even weirder,” Rouse said, according to the website Sci-News.com. “This shows us that there continue to be mysteries in the sea and there is still so much more to discover, especially since we only found these creatures 12 years ago.”
The mating process of Osedax priapus was also found to be vastly different than its predecessors. While the earlier type of Osedax males are permanently attached to their female hosts, the new species have to seek out a mate. To account for this, the males have evolved to have an extremely extendable body that allows them to reach far out (up to ten times its contracted state) to find female mating partners, Dr. Rouse explained.
Luis Georg of Perfect Science noted that the new worms were found at largely the same area of Monterey Bay that the previous species had been found 12 years ago. They are members of Siboglinidae, a family of worms that are also known as bearded worms and that live in unexpected locations, such as hot and acidic hydrothermal sea vents.
However, Vrijenhoek told Perlman that this new species “is exceptional because the genes for producing full-size adult males should have deteriorated over time because they weren’t used by the dwarf males. But apparently the genes are still there. And although those microscopic dwarf males weren’t competing with the females for food, in this much larger species they do.”
“So it’s our hypothesis that here there’s a new potential for sexual conflict, and the ability of the males to stretch themselves out like rubber bands to roam for females suggests that they’ve reinvented mating,” he added. “It’s a throwback to an earlier ancestral species more than 40 million years ago. We’re continuing to collect more species to see what their genes are telling us.”