Residency and size affect fight duration and outcome in the fiddler crab Uca annulipes

Abstract

We performed a field experiment to investigate the effect of carapace width, major cheliped length and burrow ownership on the fighting success of male fiddler crabs (Ucu mnul&r). We removed males from their burrows and released them back into the colony (n = 82). Released males tended to initiate encounters with burrow owners slightly smaller than themselves. Several general predictions of Sequential Assessment Game models of contest behaviour were supported (1) residents won more encounters; (2) intruders were more likely to win when larger than residents. When body size (carapace width) was controlled for, intruders with relatively large daws for their body size were more likely to win contests; (3) the duration of encounters was related to the Size difference between males; (4) encounters won by the larger male were of shorter duration than those won by the smaller male; (5) encounters won by the resident tended to be of shorter duration than those won by intruders (P = 0.07); (6) on average, encounter duration was longer when the intruder was larger than the resident. However, the encounters we documented began with seemingly costly behaviour such as pushing and the inter-locking of claws and did not unambiguously escalate from initial low cost behaviours. Sequential assessment of relative fighting ability may therefore not have been occurring. Prior visual assessment of opponents' fighting ability, followed by 'all-out fights' during physical encounters may also provide a plausible explanation for our results. 01996

Visual signalling and sexual selection in male fiddler crabs Uca tangeri

“…These results suggest that resident crabs capitalize on 2 advantages: claw size and a resident effect. The same pattern was shown by Jennions & Backwell (1996) in an investigation of the effect of residency and size on the fighting success of male Uca annulipes. In a series of field experiments where males were released in the colony after being removed from their burrows, the authors found that when controlling for body size, intruders with larger claws were more likely to win encounters than intruders with smaller claws, suggesting that, when body size is not a factor, claw size determines the outcome of the interaction.…”

Mutual mate choice in crayfish: large body size is selected by both sexes, virginity by males only

“…isopods Shuster, 1981;decapods, Greenspan, 1980), including crayfish (Astacus astacus, Furrer, 2004; Austropotamobius pallipes Villanelli & Gherardi, 1998;Gherardi et al, 2006;and Orconectes rusticus Berrill & Arsenault, 1984). In the majority of the species studied so far, large males are successful when competing with other males for access to females (Jennisons & Blackwell, 1996). Large crayfish males are dominant over smaller ones (Berrill & Arsenault, 1984;Villanelli & Gherardi, 1998) and more easily force females to copulate (Snedden, 1990;Gherardi et al, 2006).…”

Prey availability and selective foraging in shorebirds

“…Males have a greatly enlarged, sexually selected claw that is used in courtship and inter-male conflicts (Crane 1975;Greenspan 1975;Christy 1980;Jennions & Backwell 1996). The claw may confer some protection against avian predators because of the high handling costs associated with this potentially dangerous weapon (Bildstein et al 1989).…”