Meeting Abstract

P2.5  Tuesday, Jan. 5  The blue streak in Uca pugnax: fast, bright, and beautiful – but does it mean anything? BARNARD, M.E.*; STRANDBURG-PESHKIN, A.R.; YARETT, I.R.; MERZ, R.A.; Swarthmore College; Swarthmore College; Swarthmore College; Swarthmore College mbarnar1@swarthmore.edu

In fiddler crabs (Uca sp.), a male uses his display claw to signal his potential reproductive fitness to females and to threaten and fight with other males. In our study we explored whether the blue streak, a color bar located on the anterior carapace of both sexes of Uca pugnax, serves as another signaling device. Uca sp. are sensitive to the color blue and the streak is located in a position visible to interactive conspecifics. The presence of the blue streak is positively associated with two known sexually selected traits in males, claw length and carapace size, and it only appears as the crabs reach sexual maturity. Unlike claw length and carapace size, however, the color of the blue streak is dynamic and can vacillate between bright blue and nearly black in as little as 5 minutes. Laboratory experiments indicate that light but not temperature can mediate this response. When crabs displaying blue streaks in the daylight were moved into the dark but kept at constant temperature (31° C) they began to darken within 3 minutes and became nearly black in less than 12 minutes. Crabs exposed to a 10° C change in temperature (31 – 21° C) had no significant change in color when light was kept constant. In the field, the blue streak varies with the behavior of the crab; it is significantly brighter and bluer when the crabs are foraging away from their burrows or fighting and darker during waving displays or while the crabs are basking. The rapid changes in streak color in response to both abiotic and biotic factors strongly suggest the possibility that the blue streak could be used as a signaling mechanism in U. pugnax.