Facial band colour in the mangrove crab Parasesarma peninsulare Shahdadi, Ng & Schubart, 2018 plays a role in mate recognition

Various crab taxa are known to use their external colouration as visual courtship signals. Early research on the mangrove crab Parasesarma peninsulare Shahdadi et al., 2018 indicated a potential role in sexual signalling for its bright blue-green facial bands, which are highly conspicuous against mangrove mud. To advance this work, we conducted experiments investigating both male responses to female stimuli and female responses to male stimuli. Two sets of binary choice experiments were performed—one with live crabs and one using androgyne images where the only sex-specific cue was facial band colour—to test whether the crabs could distinguish between male and female conspecifics based on the colour of their facial band alone, i.e. independent of auditory, chemical and other visual cues. In both cases, the crabs showed a significantly greater preference for conspecifics of the opposite sex (i.e. males preferred females and vice versa). These results provide evidence for colour vision in Parasesarma and suggest that the facial bands are used by the crabs for sexual discrimination and mate recognition.