SOME CONSEQUENCES OF SEXUAL DIMORPHISM: FEEDING IN MALE AND FEMALE FIDDLER CRABS, UCA PUGNAX (SMITH).

1. There were no differences in the respiratory rates of male and female Uca pugnax of comparable sizes. 2. The amount of salt marsh sediment ingested by starved male and female crabs was similar. 3. The number and weight of fecal pellets produced by male and female crabs were similar, as was the organic matter content. 4. The above suggests that there are minimal differences in food demands and digestive efficiencies between the sexes, yet the enlarged claw of the fiddler crabs cannot be used for feeding. This requires some compensatory mechanism in male crabs. 5. Male fiddlers do show about half the feeding motions per unit time compared to females, but they compensate by feeding about twice as long. This is corroborated by field observations. 6. Further compensation, if needed, could be achieved by the slightly larger holding surface of the feeding claw in males, perhaps allowing the grasping of larger fragments of marsh sediment.