Mr. and Mrs. Crab: How Can We Tell Them Apart?

Male and female mud crabs may look alike at first glance, but clear differences in physical characteristics exist. These variations between sexes are known as sexual dimorphism. Sexual dimorphism may help species to survive in their environments. We found that three mud crab species (orange, green, and purple mud crabs) showed similar patterns of sexual dimorphism. Males generally have larger body and claw sizes, whereas females have larger abdomens. Orange mud crabs also have a unique body shape variation compared to green and purple mud crabs. All mud crabs have spines along the top edge of their shells, and scientists have numbered these spines to identify them. Unlike the green and purple species, orange mud crabs are wider at spine 8 than spine 9. Sexual dimorphism in crabs might be linked to how they reproduce and where they live.