* E-mail: aminmokhlesi@gmail.com Sexual Differences in Foraging Behavior of Fiddler Crab, Uca sindensis (Decapoda: Ocypodidae) Mokhlesi, Amin 1* ; Kamrani, Ehsan 2 ; Backwell, Patricia 3 , Sajjadi, Mirmasoud 2 1- Tehran Central Branch, Islamic Azad University, Young Researchers Club, Tehran, IR Iran 2- Department of Marine Biology, Faculty of Science, University of Hormozgan, Bandar Abbas, IR Iran. 3- School of Botany and Zoology, Australian National University, Canberra, Australia. Received: October 2011 Accepted: December 2011 © 2011 Journal of the Persian Gulf. All rights reserved. Abstract Fiddler crab females have two small feeding claws while males have only one; the other is enlarged and used as a weapon as well as a mate attraction signal. The study was conducted on the small intertidal fiddler crab Uca sindensis in the Abi estuary near Bandar Abbas on the Persian Gulf. Data were collected from September 2007 to August 2008 in order to cover a wide range of ecological conditions experienced by these crabs over the duration of a year. We considered whether males Uca sindensis have behaviorally or morphologically compensated for the loss of one feeding claw. Therefore we measured the sex ratio of surface-active crabs; the size of the feeding claws the amount of food processed and the feeding effort (male and female). We showed that males scoop up handfuls of sediment at approximately half the rate of females, but spend more time feeding than do females (70.41%). Males are slightly larger than females, but the relationship of feeding claw to carapace size is not linear: small females have relatively large feeding claws for their size, while large males have relatively large feeding claws for their size. Males and females process equivalent amounts of food on a daily basis. In order to compensate for the loss of one feeding claw, males need to spend a greater amount of time feeding. Keywords: Uca sindensis, Foraging behavior, Fiddler crab, Persian Gulf 1. Introduction Sexual dimorphism is a common phenomenon in the animal kingdom. Males may be brightly colored while females are dull (e.g. bird, Butcher 1984; Slagsvold, 2000). Males may be smaller (e.g. spiders, Elgar, 1991) or larger (e.g. most birds, reptiles and mammals, Abouheif and Fairbairn, 1997; Andersson 1994; Blanckenhorn, 2005; Dubey et al., 2009) than females or may possess exaggerated appendages that are absent in females (e.g. stag beetle, Armin, 2006; Brittany et al., 2008). There are many studies examining sexual dimorphisms in terms of sexual selection and reproductive fitness, but far fewer have examined the effect of sexually selected dimorphisms on the non- reproductive aspects of animal life, for example, its effect on foraging behavior and efficiency. An extreme case of a sexually selected dimorphism affecting feeding is found in the fiddler crab. These animals feed on algae, bacteria and decaying plant and animal matter in the mud surrounding their burrows (Caravello and Cameron, 1987; Teal, 1958). They use their feeding claws to scoop up a small amount of sediment and put it into their mouth (Icely and Jones 1978; Miller, 1961; Ono, 1965; Yamaguchi, 2000). Females have two small Journal of the Persian Gulf (Marine Science)/Vol. 2/No. 6/December 2011/7/37-44