Sex and social costs of escaping in the striped plateau lizard Sceloporus virgatus

As a predator approaches, prey base decisions about when toflee on a balance between degree of predation risk and costsof escaping. Lost opportunities to perform activities that mayincrease fitness are major escape costs. Paramount among theseare chances to increase fitness by courting and mating and bydriving away sexual rivals. Because sexual selection imposesdifferent social demands on the sexes, social opportunitiescan have different consequences for males and females, but effectsof sex differences in social opportunity costs on escape behaviorare unknown. We conducted a field experiment showing that malestriped plateau lizards (Sceloporus virgatus) given the opportunityto court or perform aggressive behavior permit closer approachbefore fleeing, but females do not. Males allowed a simulatedpredator to approach closer before initiating escape if a tetheredmale or female rather than a control stimulus was introducedto them, but females initiated escape at similar distances inall conditions. For males, a trade-off between the greater predationrisk accepted before fleeing due to the likelihood of enhancingfitness by sexual or aggressive behavior accounts for closerapproach allowed in the presence of conspecifics. Mating opportunitiesare not limiting for females in most species and females oftenhave little to gain by interacting aggressively with other females.Therefore, presence of a conspecific male or female may notjustify taking greater risk. Results confirm the predictionof optimal escape theory that flight initiation decreases ascost of escaping increases. The sex difference in effect ofpresence of conspecifics on flight initiation distance is aconsequence of the sex difference in costs of escaping.