Researchers at the University of Illinois at Chicago have discovered a chemical compound in male blue crabs that is not present in females.
Published in PLoS One, this is the first research to find an entire enzyme system activated in only one sex of a creature. The research was performed using nuclear magnetic resonance.
Lead author Robert Kleps, director of the UIC Research Resource Center NMR Lab, says that though hormone level differences are generally accepted as the primary cause of variation between the sexes in animal and human development, the existence of a sex-specific metabolite is a previously unrecognised and potentially significant biochemical phenomenon.
"It's possible to speculate that the presence or absence of a sex-specific metabolite might affect an animal's development, anatomy and biochemistry," said Kleps, adding that differences between the sexes such as susceptibility to heart disease or average life span might be due to the presence or absence of a metabolite.
He believes that with the knowledge that a sex-specific metabolite exists in one animal, researchers may now review metabolic studies in other animals and humans to look for the presence of a sex-specific metabolite that might have escaped notice in the variation among individuals.
During the study, the researchers found in an atom of P-31 with a signature "chemical shift" in male gill tissue, indicating the presence of a unique, unidentified phosphorus compound.
Upon analysis of the phosphorus compound, they identified it as 2-aminoethyl phosphonate, an uncommon but well-documented metabolite which is not known to be a hormone.
Similar results were produced when the researchers tested gill tissue from crabs harvested in six different years from the Chesapeake Bay and the gulf coast of Florida, confirming that the presence of AEP in males and absence in females is the norm for blue crabs.
Kleps, however, did not rule out the possibility that the difference between the sexes could be due to a difference in their diet.
In his papers, he has revealed 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. It 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. That blue crabs have this sex-specific compound may be a fluke, or it might represent a common but overlooked process in animal development," said Kleps.