Prey preferences of specialized jumping spiders (Araneae : Salticidae).
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
I studied prey preferences of two groups of specialized jumping spiders (Salticidae), ant-eating ('myrmicophagic') species and spider-eating ('araneophagic') species, in the laboratory. Spiders and ants have in common being unusual and dangerous prey for a salticid. Ten salticid species, four species of Portia (P. africana, P. fimbriata, P. labiata and P. schultzi) which specialize at catching other species of spiders (araneophagic species) and six myrmicophagic species (Chalcotropis sp., Habrocestum pulex, Siler sp., Telamonia masinloc, and two new species of euophryines in a new genus) were studied. Each of these specialized salticid species, whether araneophagic or myrmicophagic, uses prey-specific capture behaviour against its unusual prey and also shows pronounced preferences for these prey (ants or spiders, depending on the species). The capture behaviour of the four species of Portia was known prior to the present study, but the description of capture behaviour of the six ant-eating salticids and the data on preferences of all species are new in this study. Although all myrmicophagic and all araneophagic salticid species tested resemble each other by having prey-specific capture behaviour against ants and spiders, respectively, details of the predatory behaviour used against ants vary among the species, and the same is true for behaviour used against spiders. All Portia species studied are known to have different prey-specific capture behaviour for use against spiders and insects. Also, they are all shown in the present study to have distinctive preferences for web-building spiders over insects as prey. However, the capture behaviour of P. fimbriata from Queensland is also known to differ depending on whether the prey is a web-building spider or a cursorial salticid spider: a specialized behaviour ('cryptic stalking') is used by Queensland P. fimbriata, but not by other Portia, for catching other salticids. In the present study, Queensland P. fimbriata is known also to prefer salticid spiders not only to insects but also to web-building spiders. In contrast, the other Portia species (P. africana, P. labiata and P. schultzi) studied prefer web-building spiders to salticid spiders as prey. This study suggests that, in specialized salticids, the trend is: when a species has a special capture behaviour for a particular type of prey, it also shows a preference for that type of prey. Portia shows intersexual variation in preference. In all Portia species studied, both the males and the females behave similarly during capture sequences against spiders (i.e., use the same prey-specific capture behaviour). Also, both the males and the females of Portia are shown in the present study to have similar preferences for taxonomic categories of prey. However, there are intersexual differences in the size of prey preferred: males prefer smaller prey, and females prefer larger prey. Factors affecting intersexual differences in prey-size preference are discussed. A study of P. labiata from Los Banos in the Philippines illustrates how prey-specific capture behaviour and prey preference may interrelate at a more fine-grain level. In nature, the diet of the Los Banos Portia includes Scytodes, an unusually dangerous prey spider. Scytodes is a genus of spiders with a unique predatory behaviour: these spiders spit a sticky gum from their fangs onto prey, and onto predators. I investigated interactions between Scytodes and four species of web-invading salticids, including P. fimbriata from Queensland, P. labiata from the Philippines and P. labiata from Sri Lanka. Los Banos P. labiata, but neither Queensland P. fimbriata nor Sri Lanka P. labiata, uses a Scytodes-specific capture behaviour, and also it prefers Scytodes as prey. A brooding Scytodes, compared to a non-brooding Scytodes, is a safer prey for a Portia because the brooding Scytodes carries her eggs in her fangs, effectively blocking the spitting weapons. As an apparent refinement of its predatory strategy, Los Banos P. labiata distinctively prefers brooding Scytodes over non-brooding ones. Optimal foraging theory is considered in a discussion of the factors that may have been important in the evolution of prey preferences.