Fiddlers on the roof: elevation muddles mate choice in fiddler crabs

Abstract

Biological signaling usually occurs in complex environments, yet signals are most often studied in controlled experiments that strip away this complexity. Male fiddler crabs possess one enlarged claw that is waved during courtship displays, and females preferentially respond to larger claws and faster waves. Fiddler crab vision is evolutionarily specialized to their predominantly level mudflat habitats, although some populations inhabit topographically complex environments. Here, we investigated how the elevation of signaling males relative to receiving females affects attractiveness. Experiments with robotic crabs revealed a strong female aversion to males signaling from atop small (>2 cm) mud mounds. This aversion entirely masked previously documented strong preferences for large claws and faster waving. Our results suggest that variation in signaling environment might substantially weaken selection on males, thereby helping to maintain genetic variation in courtship traits.