Influence of cues from the anterior medial eyes of virtual prey on Portia fimbriata, an araneophagic jumping spider.

Portia fimbriata from Queensland, Australia, is a jumping spider (Salticidae) that preys on other spiders, including other salticids. Cryptic stalking (palps retracted, walking very slowly and freezing when faced) is a prey-specific tactic deployed exclusively against salticid prey. Using vision alone, P. fimbriata discriminates salticid from non-salticid prey, with the prey salticid's large anterior median (AM) eyes providing critical cues. Here, using computer-rendered virtual three-dimensional lures, we clarify experimentally some of the specific optical cues from AM eyes that influence the behaviour of P. fimbriata. Control lures were based on Jacksonoides queenslandicus, the salticid upon which P. fimbriata most commonly preys in nature. Experimental lures were modified to isolate specific combinations of AM eye features. For presentation to P. fimbriata, lures were projected on a small screen positioned in front of a web-covered platform. Each individual P. fimbriata was tested once with a control lure and once with a lure on which some AM eye feature had been altered. P. fimbriata was affected by the presence-versus-absence of AM eyes, by the size and shape of these eyes and by AM eye position. Horizontal position on the face of a single AM eye had no discernible influence on whether P. fimbriata initiated cryptic stalking, but reduced how often P. fimbriata froze when faced by the prey. The implications of the findings are discussed in relation to perceptual processes underlying the predatory strategy of P. fimbriata.