PILLAR BUILDING IN THE FIDDLER-CRAB UCA BEEBEI - EVIDENCE FOR A CONDITION DEPENDENT ORNAMENT

In the fiddler crab (Uca beebei) males build a small mud pillar next t o their burrow which increases their attractiveness to females. Three hypotheses were tested to explain inter-male variation in pillar-build ing. (1) The benefits of pillar-building are density dependent. The ex perimental addition of vertical structures did not support this hypoth esis as there was no change in the level of pillar-building. (2) There are two classes of males (pillar-builders and non-pillar-builders). T his could either be due to an alternative mating strategy, or because pillar building is age or size-dependent. There was also no support fo r this hypothesis. (3) Pillar-building is an honest signal of male qua lity dependent on body condition. A food supplementation experiment wa s performed. Addition of food affected several aspects of male behavio ur and resulted in a two fold increase in the number of pillars built between control and food treatments (P < 0.001). However, the percenta ge of males building pillars did not increase significantly. Pillar bu ilding in this species has been attributed to sensory exploitation. Ou r results indicate that a trait which may well have evolved through se nsory exploitation also appears to be condition-dependent. We emphasis e that showing that an ornament or behaviour is condition-dependent do es not necessarily mean that it evolved through ''good gene'' processe s. However, in terms of its current selective value, pillar building m ay be maintained through female choice because it acts as a signal of male condition.