Context-dependent running speed in funnel-web spiders from divergent populations

P>1. Locomotor performance can influence individual fitness through several ecological contexts, such as prey capture and predator escape. One means of determining which contexts act as significant selective forces on running speed is to quantify individual speed in each context. The underlying hypothesis is that animals will exhibit their highest speeds in contexts most crucial to fitness. 2. We measured running speeds in three ecological contexts (prey capture, fleeing predators and territory defence) in lab-reared offspring of the funnel-web spider Agelenopsis aperta collected from two arid grassland and two riparian populations. Arid populations experience little predation pressure, are prey limited, and are highly territorial; riparian populations experience high predation, have high prey availability, and are less territorial in nature. 3. The offspring of arid individuals exhibited their highest burst speeds in territory defence, and ran more slowly in response to predator threats. The offspring of riparian populations, however, ran fastest when responding to predatory threats and displayed lower velocities in prey capture and territory defence. Thus, our findings support the hypothesis that A. aperta are selected to exhibit their highest speeds in contexts most important to their fitness. 4. Contextual use of running speed can differ among conspecific populations experiencing differing selective forces on locomotion.