Fighting strategies and mechanisms behind contest resolution in the jumping spider Servaea incana

Contests over limited resources are commonplace and widespread across animal taxa. Rather than unconstrained fighting, animals are expected to adopt strategies designed to reduce contest costs. One such strategy is mutual assessment, where each rival performs ritualised signals of fighting ability or resource holding potential (RHP), allowing animals to economically determine which is weaker. However, as assessment itself may also be costly or difficult, an alternative strategy to limit the costs associated with contests may be for rivals to persist until they reach an internal cost-threshold. Each strategy allows for determination of the winner while limiting the costs of fighting. Jumping spiders, with their excellent vision, elaborate displays and dangerous weapons present excellent models for the study of decision making in animal contests. In this thesis I describe the biolgy of the jumping spider Servaea incana and examine the decision rules used in the male-male contests. Size is a strong predictor of contest outcome and also of whole-organism performance capacity. Correlations between size and levels of contest escalation suggest that smaller spiders are less willing to escalate, regardless of opponent size, and this suggests use of internal thresholds rather than mutual assessment. Video playback experiments reveal that visual assessment of opponent size may influence the decision to display towards or approach an opponent. Hunger may also influence contest behaviour; hungry spiders are more likely to attack conspecifics and may be more likely to engage in contests. The potential for injury, or even death, may explain the unwillingness of small spiders to engage in escalated contests.