Like car wash attendants for the coral-reef crowd, Lysmata shrimp staff "cleaning stations" where fish can go to be shined up. At these stations, cleaner shrimp eat parasites and dead tissue off the bodies of their clients, while the fish repay the act by not eating the shrimp. Some cleaner shrimp species, such as L. amboinensis, live and work in monogamous, hermaphroditic couples, faithfully fertilizing each other's eggs during their off-hours. In order to arrive at these peaceful unions, however, they might have to do a little killing.
Researchers Janine Wong and Nico Michiels in Germany wanted to know how L. amboinensis ends up in pairs rather than groups. When everybody has all the equipment necessary to spawn more shrimp, why is two the best number to live in?
The researchers collected cleaner shrimp subjects and kept them in tanks one, two, three, or four at a time. No matter ...
