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.

招潮蟹（fiddler crab）中的角状招潮蟹（Uca capricornis），其相邻雌雄个体间存在独特的社会关联。本实验旨在探究雄蟹对其洞穴附近被束缚的个体的行为响应模式。研究人员观察了雄蟹对相邻个体与陌生个体（二者物理特征相近）的响应行为。当目标雄蟹（focal male）触碰被束缚的个体（tethered individual），记为“接近”行为，或经过5分钟仍未发起接近，记为“忽视”行为时，本次试验即告结束。两次试验分别对应相邻个体与陌生个体，其开展顺序为随机设置。本实验共完成80组，其中以下4种组合各20组：i）雄蟹-相邻雄蟹；ii）雄蟹-陌生雄蟹；iii）雄蟹-相邻雌蟹；iv）雄蟹-陌生雌蟹。
实验结果表明，雄蟹对相邻雌蟹的处理方式与对相邻雄蟹及任意性别的入侵者均存在显著差异。相较于被束缚于同一位置的陌生雌蟹，雄蟹接近相邻雌蟹的概率更低。而雄蟹对陌生雌蟹、相邻雄蟹与陌生雄蟹的接近概率并无显著差异。