Milner, R. N. C., Jennions, M. D., Backwell, P. R. Y. 2008. Does the environmental context of a signaling male influence his attractiveness? Animal Behavior 76: 1565-1570.

The recent lecture on Mating Games and Signaling looked at different mechanisms for mate attraction and signal detection from a distance. In order for a visual signal to be effectively received by a potential mate it must be noticed and detected against the background environment. The authors of this paper used a robotic fiddler crab in order to examine the differences in fiddler crab background environments and how that influences the conspicuousness of the males’ visual display, and in turn his attractiveness to potential mates.

The male fiddler crab (Uca mjoebergi) waves his enlarged claw as a means to attract females as they pass by his territorial burrow. The males display in a variety of different habitats, from open mudflats to those shaded by mangrove trees or amongst the mangrove roots. Previous papers cited in this article note that females select males based on a number of specific male traits, and an unpublished citation notes that males with bigger claws and higher wave rate are observed to be selected more in the wild, although for this study they didn’t vary the wave rate.

For this study transects of shoreline were surveyed and the habitat around the males’ burrows was scored based on amount of shade, the presence of mangrove roots, and the presence of shells and leaves. For the experiment they selected an area of environmentally homogenous habitat and relocated all crabs within 2m of their arena. A female was kept in a clear container and watched two identical robotic males display, and then released to see her mate choice preference to ensure that there was no side bias. They then performed a number of experiments testing the female’s preference after altering the environment with either shade, differences in background pattern, or bamboo to simulate the presence of mangrove roots.

The authors found no significant effect of environmental manipulation. The female showed no preference for males regardless of the environment, including the manipulation of foreground noise in the form of mangrove roots, which partially obscured the male’s claw. They do mention that these findings corroborate recent work that indicates that females pay attention to color differences, which is offered as a possible alternative explanation for the results. The authors discuss the spectral sensitivity of four other fiddler crab species, but have no direct data on the one used in this study. Another alternative explanation is the female preference for specific habitats, so she might be selecting a male based on where he is signaling from. The authors also acknowledge that the female may be adapted to notice the claw wave regardless of environmental noise. I thought that the authors made perhaps too large of a jump between a signal being conspicuous and being attractive to a potential mate.