Optical cues and vision-based discrimination mechanisms underlying predatory versatility in jumping spiders (Araneae: Salticidae).
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Experimental studies of behaviour were carried out on jumping spiders (Salticidae), with particular attention given to araneophagic species in the genus Portia. Portia fimbriata was the primary species used in experiments. The objective of the research was to clarify mechanisms underlying visual perception, with this being part of a larger aim of understanding animal cognition. Literature on the structure and function of salticid eyes was reviewed in depth, with hypotheses and directions for future work highlighted. Distances at which salticid species distinguish prey insects from conspecific rivals was investigated using adult males of 37 salticid species. The discrimination distances recorded for most species imply higher levels of spatial acuity than has generally be appreciated for salticids. The longest discrimination distances found were for Mogrus neglectus, (max. 320 mm or 42 body lengths), with Portia fimbriata coming close (280 mm or 47 body lengths). P. fimbriata is unique among Portia spp.: all species of Portia prey routinely on other spiders (araneophagy), but P. fimbriata also has a specialised method of stalking and capturing other salticids. Optical cues by which P. fimbriata distinguishes salticid from non-salticid prey were investigated. P. fimbriata’s reactions to 114 salticid species were established. Except for Myrmarachne spp. (ant mimics), all salticids (both sympatric and allopatric species, species with aberrant body form and highly camouflaged species) triggered salticid-specific tactics by P. fimbriata. Experiments with odourless lures made from dead prey on which various combinations of features were altered imply that the large principal eyes of salticid prey provide optical cues that are critical for triggering P. fimbriata’s salticid-specific predatory tactics. Cues from the legs of prey salticids influence whether P. fimbriata’s stalks at all, but not whether salticid specific tactics are adopted. Cues from the cephalothorax and abdomen also influenced stalking tendency, but more weakly than cues from the legs. Using specially developed virtual 3D lures, presented to P. fimbriata on a projector screen, details concerning cues from the principal eyes of salticids were investigated. To be identified as a salticid, evidently there must be at least one principal eye on the face that is large and round. P. fimbriata distinguishes the orientation of salticid prey. A hypothetical model of how P. fimbriata distinguishes salticid orientation is discussed. That Portia spp. distinguishes the orientation of other non-salticid web-building spiders is also established in experiments where live prey is used. Using lures made from Badumna longinquus, a web-building spider, orientation-revealing optical cues were investigated. The research in this thesis suggests a framework for future studies.