The effects of spatial context and social experience on the territorial aggression of male threespine stickleback

1. Territorial male threespine stickleback, Gasterosteus aculeatus, attacked their neigh burs more and escaped fi om their neighbors less when at their own nests than when at their neighbors' nests. In this study, attacks decreased gradually and escape attempts increased gradually as males moved from the center to the edge of their territories. 2. As predicted by the conflict hypothesis, males performed head-down threat displays most at their tc territory boundaries. The conflict hypothesis holds that aggression and fear are two opposing tendencies that regulate the expression of attack and escape behavior. 3. This experiment did nut find evidence for a threshold effect of aggression or fear in which new behaviors would abruptly replace attack or escape once a certain level of motivation had been activated. 4. Males in our study that had social experience outside of their territories, either fighting with a rival or spending time with a sympatric heterospecific. made fewer attacks overall in later encounters with their neighbors in their and their neighbors' territories than did males without social experience. This finding demonstrates that the influence of encounter site on territorial aggression is modified by a male's past experience. 5, Males with winning and losing experiences outside of their territories did not respond differently to their neighbors in later encounters.