They then isolated and analyzed the phosphorus compound, identifying it as 2-aminoethyl phosphonate, an uncommon but well-documented metabolite. AEP is not known to be a hormone.
The researchers tested gill tissue from crabs harvested in six different years from the Chesapeake Bay and the gulf coast of Florida. Specimens from each region produced similar results, confirming that the presence of AEP in males and absence in females is the norm for blue crabs.
But, Kleps said, it was still not possible to rule out that the difference between the sexes was due to a difference in their diet. Fortunately, while writing the first draft of the paper, Kleps happened to read that a rare gynandromorphic blue crab -- one half male, one half female -- had been captured by Romuald Lipcius of the Virginia Institute of Marine Science at the College of William & Mary.
The rare gynandromorph is divided down the middle, with a characteristic blue male claw and a female red claw. The underside of the crab is also visibly divided into male and female halves. After the crab died, Lipcius sent Kleps gill tissue from each side for analysis. The measured levels of AEP from the male and female gills provided additional evidence that AEP is a sex-specific compound.
"Since both sides of this strange crab have, of necessity, shared a diet and environment, we had completely independent confirmation of the sex-specific nature of this metabolite," said Kleps.
"That blue crabs have this sex-specific compound may be a fluke, or it might represent a common but overlooked process in animal development," he said.
|Contact: Jeanne Galatzer-Levy|
University of Illinois at Chicago