Conditional strategies in the intraspecific interactions of salticid spiders : why fight ?
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Salticid spiders have exceptionally intricate display behaviour during interactions between conspecific individuals. That courtship (male-female display) is related to intersexual selection appears to be well established, but the function of intrasexual display remains poorly understood. My objective was to clarify the external variables that influence the decision rules of salticids during intrasexual interactions. Three species of salticids were tested: Euophrys parvula from New Zealand, and Jacksonoides queenslandicus and Portia fimbriata from Australia. Intrasexual conflict was observed between pairs of salticids in the presence and absence of optical or olfactory cues from potential resources (mate and prey). When displays escalated more often in the presence of a resource, compared with the absence of these cues, it was viewed as competition for the resource. Movement alone, in the absence of other cues, does escalate competitions between male E. parvula and is an important control in determining the value of resources. Although male salticids escalated intrasexual competitions in the presence of visual and/or olfactory cues from conspecific females, female salticids did not escalate competitions in the presence of cues from conspecific males. However, female, but not male P. fimbriata did escalate intrasexual interactions in the presence of olfactory cues from a common prey species, J. queenslandicus. These results support predictions from sexual selection theory that females are a valuable resource to males and that intrasexual selection may have shaped the decision rules used during male-male competition in salticids.