Female mate choice in the fiddler crab Uca mjoebergi

Female mate choice is an important force of sexual selection. Males of countless species have evolved extraordinary traits solely to increase their attractiveness to females. Several factors can, however, affect a female's degree of choosiness for these traits. Variation in mate choice can have several important evolutionary consequences for both sexes. In this thesis, I examine factors that can influence female mate choice and male mating success in the fiddler crab Uca mjoebergi. Fiddler crabs live in dense, mixed sex colonies where each individual occupies and defends a burrow that is essential for survival. During predator attacks, males and females will retreat quickly into their burrows for safety. I found that time spent in a refuge was highly flexible and strongly dependent on the trade-off between the costs and benefits of hiding in U. mjoebergi. Males and females took longer to re-emerge when foraging opportunities were low. Furthermore, when mating opportunities were experimentally increased, actively courting males engaged in highly risky behaviour. Interestingly, re-emergence times were not correlated with size. I therefore examined whether time spent in a burrow after a predation attack (risk-taking behaviour) predicts aggression, surface activity levels and mating success in males. Risk-taking behaviour was highly consistent among individuals. Males that took greater risks with predators also behaved more aggressively when searching for a new burrow, and experienced a higher mating success compared to their shy counterparts. This study suggests that non-sexually selected traits, such as risk-taking, may represent important behavioural predictors of male success in other contexts for numerous species. I then examined the effect of claw regeneration on male territory ownership and mating success. Males often lose their major claw in combat or as a predator avoidance -ivtactic. Males regenerate a claw that is much weaker and lighter than the original claw and is therefore a less effective weapon. Although claw regeneration did not affect signal quality, males with regenerated claws were less likely to acquire and defend high quality territories and consequently suffered a decrease in mating success. Mate choice in fiddler crabs is based on the sequential assessment of multiple male traits. To assess males, receptive females leave their burrows and visit several courting males, initially deciding to visit males based on their size and wave rate but making their final mate decision based on burrow quality. Uca mjoebergi occurs in habitats that are inundated only by the highest amplitude spring tides. Larval release outside these tides will result in complete failure of reproductive effort. 1 show that females adjust their preference for the direct benefits of mate choice to increase their reproductive success by selecting burrows to influence incubation rate and ensure timely release of their larvae. Using a robotic crab system, I then investigated if the social context in which males are assessed influences female preference. Females can encounter a number of potential mates simultaneously before making a mate choice decision, calling into question whether the attractiveness of one male depends on the attractiveness of the other males a female has previously encountered. The presence of an asymmetrically dominating decoy, however, did not significantly alter the relative preferences for the two options. 1 suggest that the reliability of each sexually selected trait in a complex signalling system potentially masks the effects of context-dependent mate choice. Lastly, 1 explored why males wave synchronously at females. Again, using robotic male crabs, 1 show that females have a strong preference for leading waves, and intense competition by males to wave first has resulted in this highly synchronised display.