The function of colourful facial bands in mangrove crab (Perisesarma) communication

Abstract

Bright colours are a key visual signal in many animal communication systems. Here we examine the function of the blue-green facial bands found in two species of mangrove crabs, Perisesarma eumolpe (De Man) and P. indiarum (Tweedie). Food (mangrove leaves) deprivation and re-feeding experiments demonstrated that facial band brightness and saturation changed significantly with nutritional status. These results suggest that the colours are diet-derived and could be carotenoid-based. Manipulation of the facial bands had significant effects on inter-crab behaviour. When P. indiarum and P. eumolpe males were given a choice between a female with its facial band blacked out and a similar-sized control female with natural colour, they consistently chose the latter. In a resource holding potential (RHP) experiment, male crabs defending burrows responded differently to male con-specific intruders with blacked out facial bands compared to non-blacked out controls. Together, the results show that brightly coloured facial bands in P. eumolpe and P. indiarum are important for communication; either as a way to identify conspecifics, or to convey nutritional status and hence physical quality.