Cooperation and conflict : sociality in salticid spiders.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
By studying salticid spiders from East Africa I look at sociality from an unusual perspective. These particular salticids form mixed-species groups, with more than one species and even more than one genus routinely living together within any single nest complex. The primary occupants of these nest complexes are three species of Menemerus, two species of Pseudicius, Myrmarachne melanotarsa (Wesolowska and Salm, 2002), Parajotus cinereus (Wesolowska, 2004), and an unidentified species that I call the 'Nun'. Adult males and females, along with juveniles of different age classes, share nest complexes. The highly varied composition of these groups suggests that the benefits to the salticids of grouping extend beyond species boundaries. Relatedness may not be so critical for understanding the dynamics of these inter-spider relationships. This suggests a departure from how social spiders have been studied in the past. Often Portia africana (Simon, 1886) is also a part of the nest-complex community. Although solitary as an adult, P. africana has a social juvenile phase, and juveniles of P. africana sometimes even share prey. The cues that P. africana use when making decisions to join others and cooperate in prey ambush suggests at least rudimentary numerical ability in these spiders. Myrmarachne melanotarsa, a new species described during this study, is a myrmecomorphic salticid that lives in close proximity to the ant it mimics, a species of Crematogaster. Links between the biology of the ant the ant mimic are investigated. Access to honeydew and defence by collective mimicry appear to be unusual, but especially important, aspects of this species' biology. M melanotarsa is also routinely found living close to other salticid species, and it has a preference for juveniles of other salticids as prey. Clustering with reproductive groups of other salticids appears to be important as a means by which M melanotarsa gains access to this unusual prey. Yet another social salticid species, Menemerus sp. A, has a special relationship with ants. It steals prey from foraging ants. Besides ants, two assassin-bug species (Reduviidae), Scipinnia repax and Nagusta sp., associate with the social salticids. Both feed by preference on salticids. S. repax also singles out Nagusta sp. as prey. For the salticids, one advantage of living in nest complexes appear to be that the large silk edifice a group of salticids may build provides partial protection from predators such as ants and reduviids. Experiments show that social salticid species actively choose to group with other conspecifics and with social salticids from other species and genera. However, aside from M melanotarsa, all of the social salticid species are averse to joining nest complexes containing ants. The adaptive significance of the array of different relationships and interactions within the nest complexes is discussed.