When to flee? The economics of sneakers facing territorial aggression.

In species with alternative reproductive tactics, territorial males (guarders) are usually vigilant against sneakers, and aggressively attempt to eliminate them, imposing serious costs (injuries, sometimes death). Here I examined how sneakers escape from territorial attack in the triplefin blenny, Enneapterygius etheostoma , in the field, with the help of economic flight theory developed for predator–prey interactions. Sneakers hide around spawning sites for sneaking, but they are often detected and attacked by territorial males. Fleeing soon after the initiation of attack could reduce the risk of injuries. However, fleeing may be the wrong decision, resulting in a loss of benefit that could have been obtained by not fleeing, because of uncertainty about whether the sneaker is targeted. As the guarder–sneaker distance decreases, the target would become clear, and uncertainty is reduced accordingly. Therefore, it is predicted that flight initiation distance (FID, the predator–prey distance when escape begins) is determined by the cost–benefit balance. Two types of territorial aggression were identified: the ‘direct approach’, where the territorial male directly approaches a given sneaker, and the ‘reoriented approach’, where the territorial male turns to reorient and approaches it following an attack against the first target. A field study showed that sneakers fled earlier in the reoriented approach than in the direct approach. Model selection showed that FID in the reoriented approach was predicted by the guarder–sneaker distance at attack initiation (starting distance) alone, whereas FID in the direct approach was predicted by starting distance, the interaction between the approach speed of territorial males and the duration for which the sneakers monitored them. These results suggest that sneakers adjust flight decision rules to attack episodes, i.e. the economic decision in the direct approach, but the flush early decision in the reoriented approach. This study provides a novel example of adaptation in sneakers. [ABSTRACT FROM AUTHOR]