Neighbour-stranger relations in the fiddler crab Uca capricornis

A unique relationship exists between neighbouring males and females in the fiddler crab Uca capricornis. This experiment was designed to demonstrate how a male fiddler crab responds to different individuals tethered near to his burrow. The response of a male crab to the neighbour and a stranger (with similar physical characteristics) was observed. The trial ended when the focal male touched the tethered individual (approach), or after 5 minutes passed with no approach (ignore). The order of the two trials (neighbour or stranger) was random. 80 experiments were conducted in total, 20 of each of the following combinations: i) male -- neighbouring male, ii) male -- strange male, iii) male -- neighbouring female, iv) male -- strange female.

The results indicate that males treat female neighbours differently to male neighbours and intruders (of either sex). They were less likely to approach a female neighbour than an unknown female tethered in the same spot. They were equally likely to approach an unknown female, a neighbouring male and an unknown male.