The effects of claw regeneration on territory ownership and mating success in the fiddler crab Uca mjoebergi

Underlying male quality is often reflected in the condition of sexually selected traits. In fiddler crabs, male success in both intra- and interspecific interactions is highly dependent on the size of the major claw. However, males are often forced to autotomize their major claw. Claw regeneration significantly altered the structure of a males' major claw in Uca mjoebergi. We found, however, that claw regeneration did not affect signal quality. Both males and females were unable to visually distinguish a regenerated claw from an original claw. Although regenerated males were inferior fighters, males were able to compensate for this fighting disadvantage by avoiding fights with other males. Regenerated males were, however, less likely to acquire and defend high-quality territories and consequently suffered a decrease in mating success

Colouration and Colour Changes of the Fiddler Crab, Uca capricornis: A Descriptive Study

Colour changes in animals may be triggered by a variety of social and environmental factors and may occur over a matter of seconds or months. Crustaceans, like fiddler crabs (genus Uca), are particularly adept at changing their colour and have been the focus of numerous studies. However, few of these studies have attempted to quantitatively describe the individual variation in colour and pattern or their adaptive significance. This paper quantitatively describes the colour patterns of the fiddler crab Uca capricornis and their ability to change on a socially significant timescale. The most dramatic changes in colour pattern are associated with moulting. These ontogenetic changes result in a general reduction of the colour pattern with increasing size, although females are more colourful and variable than similarly-sized males. Uca capricornis are also capable of rapid colour changes in response to stress, but show no endogenous rhythms associated with the semilunar and tidal cycles commonly reported in other fiddler crabs. The extreme colour polymorphism and the relative stability of the colour patterns in Uca capricornis are consistent with their use in visually mediated mate recognition

Social Monogamy in a Fiddler Crab, Uca Capricornis

Fiddler crabs are generally considered polygamous as they tend to live in dense mixed sex colonies with numerous neighbours and individually defended territories. We show that the Australian fiddler crab, Uca capricornis, is socially monogamous based on behavioural experiments and observations of neighbouring males and females. The unusual relationship between neighbouring males and females in U. capricornis is selected for and maintained by intrasexual aggression and the ability to recognise and defend their partner.This work was supported by an ANU PhD Scholarship with an additional contribution by the Centre for Visual Sciences (to T. D.) and an Australian Research Council grant (to P. R. Y. B.

The fiddler crab Uca mjoebergi uses ultraviolet cues in mate choice but not aggressive interactions

The perception of ultraviolet light and its role in communication has received a great deal of attention in recent years. Although ultraviolet light is no different to other wavelengths in many respects, its role as a signal does deserve special consideration, if only because it is frequently overlooked by human observers who are unable to see it. Studies on the role of ultraviolet cues in inter- and intrasexual interactions are still rare, and generally focused on vertebrates with relatively complex visual systems. Here we show for the first time that crustaceans, with a relatively simple, probably dichromatic, visual system, also use ultraviolet cues in mate choice. We found that the enlarged claws of male Uca mjoebergi reflect ultraviolet wavelengths of light. Mate-searching females preferred ultraviolet-reflecting males over those whose reflectance was blocked with sunscreen. Conspecific males showed no such preference when deciding which rival to attack, suggesting that ultraviolet cues are not involved in signalling competitive ability

When and Why Do Territorial Coalitions Occur? Experimental Evidence from a Fiddler Crab

Neighboring territory owners are often less aggressive toward each other than to strangers ("dear enemy" effect). There is, however, little evidence for territorial defense coalitions whereby a neighbor will temporarily leave his/her own territory, ente

Female fiddler crabs settle for less: the travel costs of mate choice

Females often have strong preferences for the most attractive males that provide the greatest benefits. However, searching for and sampling potential mates is costly. Females are therefore expected to make an optimizing choice whereby the benefits provided by the male outweigh the cost of choosing him. Consequently males should benefit by minimizing costs experienced by sampling females, or by reducing the ability of females to assess these costs. We investigated the economics of female mate choice in the fiddler crab Uca mjoebergi through observation of natural mate-searching behaviour, and by manipulating the costs of choice in a series of two-choice experiments using robotic crabs. Observed females were choosy about their mates, but this selectivity declined when predation risk increased. Experimental females were allowed to choose between males of different attractiveness at a range of distances from the female, with the more attractive male placed further from the female. Females did not travel further to reach a more attractive male except when distances were small. These results suggest that greater attractiveness does not always ensure greater mating success for males, as distant males experience a disadvantage. Male mate-attracting behaviour was then investigated, as male U. mjoebergi often leave their territories to approach sampling females, behaviour that may overcome a distance disadvantage. Males closely approached females regardless of their distance from the female. This behaviour is likely to prevent females from making the optimal choice, as they cannot include travel costs in their assessment of males

Hunting and predation in a fiddler crab

Fiddler crabs are known primarily to be deposit feeders. They eat detritus, bacteria, and other small particles of organic material found in the sandy or muddy substrate on which they live. They have highly specialized mouthparts used to separate edible matter from nondigestable material. Here we provide evidence of cannibalism and predation in a fiddler crab, Uca annulipes. We additionally provide the first evidence of a fiddler crab hunting shrimp and insects. This study is an exemplary reminder that, even though an animal may have evolved highly specialized feeding traits, this need not preclude it from opportunistically acting as a generalist feeder

Sex, size and colour in a semi-terrestrial crab, Heloecius cordiformis (H. Milne Edwards, 1837)

We investigated the relationship between sex, size and colour in the little studied Australian endemic semaphore crab, Heloecius cordiformis, and related it to the crabs' social system with the aim of identifying the potential signalling function of cla