Differential selection on sprint speed and ad libitum feeding behaviour in active vs. sit-and-wait foraging spiders

1. Many animals are adapted for a 'feast or famine' existence, and will opportunistically engage in gluttonous foraging bouts. However, how gluttonous feeding influences individual performance (e.g. running speed) and the fitness consequence of modified performance are not frequently considered. 2. Using laboratory track trials I establish baseline locomotor performances (burst speed) for four spider species: two active foragers (Hogna helluo and Schizocosa ocreata (family: Lycosidae)), and two sit-and-wait foragers (Agelenopsis emertoni and Barronopsis texana (family: Agelenidae)). I then fed each species ad libitum, assessed what influence this meal had on individuals' burst speed relative to baseline performance, and performed a field census to assess selection on running speed for all four species. 3. Sit-and-wait foragers fed significantly more than active foragers and slowed significantly after feeding; however, neither active forager was slowed by their meal. 4. My field census detected no selection on speed for sit-and-wait foragers, and positive directional selection on speed for both active foragers. 5. The negative association between the amount of food consumed and selection on burst speed suggests that selection pressures to maintain locomotor performance may set an upper limit to how much an animal can, or will, eat during a foraging bout.