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1.  Keeping up appearances: male fiddler crabs wave faster in a crowd 
Biology Letters  2011;8(2):176-178.
Courtship displays are often energetically and temporally costly as well as highly conspicuous to predators. Selection should therefore favour signalling tactics that minimize courtship costs while maintaining or increasing signal attractiveness. In fiddler crabs, males court females by waving their one greatly enlarged claw in a highly conspicuous and costly display. Here, we investigate whether courting males adjust their wave rate, and therefore the cost of courtship, to the current level of competition. We show that display rate increases as competition increases and that when competition is removed, males reduce their display rate by 30 per cent. These results suggest that male fiddler crabs actively reduce the cost of courtship by adjusting their wave rate in response to the immediate level of competition.
PMCID: PMC3297407  PMID: 22031721
animal communication; courtship competition; fiddler crabs; mate attraction; Uca annulipes
2.  Eavesdropping in crabs: an agency for lady detection 
Biology Letters  2010;6(6):755-757.
Although conspicuous courtship displays are an effective way of attracting the attention of receptive females, they could provide valuable information to rival males on the location of these females. In fiddler crabs, males that see a receptive female wave their single, greatly enlarged claw in a highly conspicuous courtship display. We test whether other males use this courtship display to alert them to the presence of receptive females that they cannot directly see. We show that male fiddler crabs (Uca mjoebergi) eavesdrop on the courtship displays of nearby males to detect mate-searching females. This allows males to begin waving before a female becomes visible. Furthermore, males appear to adjust their waving according to the information available: eavesdropping males wave 12 times faster than non-courting males but only 1.7 times slower than males in full visual contact with the female.
PMCID: PMC3001374  PMID: 20519196
animal communication; eavesdropping; fiddler crabs; mate attraction; Uca mjoebergi
3.  Interspecific assistance: fiddler crabs help heterospecific neighbours in territory defence 
Biology Letters  2010;6(6):748-750.
Theory predicts that territory owners will help established neighbours to repel intruders, when doing so is less costly than renegotiating boundaries with successful usurpers of neighbouring territories. Here, we show for the first time, to our knowledge, cooperative territory defence between heterospecific male neighbours in the fiddler crabs Uca elegans and Uca mjoebergi. We show experimentally that resident U. elegans were equally likely to help a smaller U. mjoebergi or U. elegans neighbour during simulated intrusions by intermediate sized U. elegans males (50% of cases for both). Helping was, however, significantly less likely to occur when the intruder was a U. mjoebergi male (only 15% of cases).
PMCID: PMC3001383  PMID: 20534601
cooperative defence; interspecific; neighbour; territory; Uca
4.  Safe sex: male–female coalitions and pre-copulatory mate-guarding in a fiddler crab 
Biology Letters  2009;6(2):180-182.
In fiddler crabs both males and females defend territories that are essential for survival. Given pronounced sexual dimorphism in weaponry, how do weaponless females defend their territory from well-armed males? Using observational data and two simple experiments, we test whether male Uca annulipes protect their female neighbours from conspecific intruders. We show that males defend their female neighbours against male but not female intruders. We also show that females sometimes mate with their immediate neighbours. Male defence of female neighbours appears to represent both pre-copulatory mate-guarding and a territorial coalition. Males who ensure that their neighbour remains female could benefit through increased opportunity for future reproductive success and lower boundary maintenance costs.
PMCID: PMC2865039  PMID: 19889695
coalitions; female protection; Fiddler crabs; mate-guarding; mating benefits; surface-mating

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