BIOLOGY

Ladies' Lunch
It's strictly the females who line up at this buffet.

Robert Vrijenhoek went looking for some clams and instead discovered something that belongs in the Hall of Very Weird Animals.
 
He was on a research ship floating 20 miles (30 kilometers) off the coast of California, above Monterey Canyon. It was February 6, 2002, and 9,000 feet (3,000 meters) below, a robotic submersible surveyed the seafloor, desolate but for a little algae and the occasional clump of grass or rogue plastic bag. Suddenly the camera glimpsed the carcass of a whale colonized by worms with red, feathery protrusions. The sub nabbed some bones for a closer look. 

The worms looked a bit like the tube worms that live around deep-sea vents, only they were much smaller. Vrijenhoek named the new genus Osedax, meaning "bone devourer." They'd been feeding on the ribs of a 30-foot-long (nine-meter-long) gray whale that had sunk to the depths of the canyon (such a carcass is called a whale fall). "If there's something to eat, somebody will find a way to eat it," Vrijenhoek says.
 
All of these Osedax scavengers, however, turned out to be females. Where were the males?
 
The mystery took two years to solve. An Australian researcher named Greg Rouse identified microscopic "sperm packages" inside the female worms' tubes. Further inquiry revealed that the packages were the males, little sperm factories living off blobs of yolk. "They just sit there giving sperm to the female until their yolk runs out," Rouse says.
 
Sexual dimorphism—where males and females exist in different forms—is common in the natural world. In humans, males are just slightly bigger than females. In some anglerfish species, on the other hand, the male is comically petite, attaching himself to the female and withering away, leaving only his testes.
 
Vrijenhoek says he knows of no sexual dimorphism as extreme as in Osedax. The males live their whole itty-bitty lives inside the tubes of the females, servicing their reproductive needs in an otherwise thankless existence.
 
Obviously this is, for some of us, a cautionary tale. Ladies, don't get any ideas.

—Joel Achenbach
Washington Post staff writer