Previous experience matters in the stalk-eyed fly <Emphasis Type="Italic">Teleopsis dalmanni</Emphasis>

Previous experiences can play a significant role in determining future behaviors. Winner and loser effects, where the outcome of previous aggressive encounters influences the behavioral approach to and outcomes of future conflicts, have been documented in many taxa and illustrate this phenomenon. These effects are prevalent in species that interact frequently because modulation of these potentially costly social interactions may influence fitness. Stalk-eyed flies of the dimorphic species Teleopsis dalmanni engage in frequent fights over food resources, as well as over access to harems of females, with larger males typically prevailing when size disparities exist. However, whether and how prior experience influences fighting decisions and outcomes remains unexplored. To test for winner and loser effects in stalk-eyed flies, sexually mature flies were paired in size-mismatched dyads to establish winning and losing experiences. After their first contest, the flies were paired with size-matched individuals and allowed to interact. We determined whether an initial winning or losing experience significantly altered the outcome probabilities in the second size-matched encounter. Initial winning experience did not significantly affect the second interaction, providing no evidence for a winner effect. However, initial losers were significantly more likely to lose a subsequent interaction which provides evidence for a loser effect in stalk-eyed flies. In addition, smaller males experienced an increased probability of losing their second interaction regardless of prior winning or losing experience. This effect was not seen in large males. Our data suggest that the loser effects we observed, which were more pronounced in small males, could result from the energetic costs of fighting that they were less able to absorb than large males.