A study published today in Current Biology reveals a new species of marine bone-eating worm whose mating system defies what scientists thought they knew about this already bizarre creature.  Unlike previously discovered species, these males are the same size as females.

When Osedax worms were first discovered 12 years ago, only females were found, feasting on bones deep in the ocean.  The males were all dwarfs, permanently attached to females’ tubes in groups like harems.

Western Australian Museum Senior Research Scientist Nerida Wilson was part of the expedition that made the new discovery 700 metres below the ocean’s surface off the coast of California and Oregon in the United States.

“It is an evolutionary surprise that the males we found were the same size as females,” Dr Wilson said.

“Females of the new species are roughly the same size as other Osedax species, but the males are tens of thousands of times larger.”

Dr Wilson joined researchers from Scripps Institution of Oceanography, the University of Copenhagen and the Monterey Bay Aquarium Research Institute on the expedition.  The lead author is Scripps Institution of Oceanography marine biologist Greg Rouse.

“This is the first known example of such a dramatic evolutionary reversal from dwarf males,” Professor Rouse said.

“This discovery demonstrates that the underlying genes needed to make a full-sized animal are still fully functional, and haven’t been lost or co-opted over time,” Dr Wilson said.

The new species is named Osedax priapus after the mythological god of fertility, because the males extend their bodies ten-times their usual state to find females to mate with.

No Osedax species have yet been found in Australian waters.  Dr Wilson is hoping to change that, and is currently liaising with oceanographers to deploy bone samples on the seabed to attract these bone-drilling worms, which would then be analysed at the WA Museum.

“Given our diverse pinniped and whale fauna, the existence of many new Osedax species would be predicted,” she said.

This research was funded by the David and Lucile Packard Foundation via MBARI, Scripps Institution of Oceanography, National Science Foundation, and the Faculty of Science at the University of Copenhagen.

 

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Western Australian Museum

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