Spoils of war and peace: enemy adoption and queen-right colony fusion follow costly intraspecific conflict in acacia ants

摘要

Intraspecific conflicts over vital limited resources can lead to costly fights, which may leave victors at subsequent risk of fitness costs through diminished defensive capability or resource holding capacity. How victors compensate for potential costs and minimize the threat of Pyrrhic victory is not well known. We tracked the outcomes of experimentally induced field conflicts between highly territorial acacia ant Crematogaster mimosae colonies. We provide evidence that the victors of colony fights have reduced worker forces to defend larger territories. Field assays indicate that postfight colonies are more vulnerable to heavy browsing of host trees by mega-herbivores and takeover by competitors following conflict. Using molecular genetics, we discovered that fatal fights significantly decrease within-colony worker relatedness. We find that reduced relatedness can be explained by colonies increasing worker number via 1) non-kin enemy adoption or 2) queen-right colony fusion. We hypothesize that incorporating non-kin enemies can speed recovery from conflict when resource defense is paramount. In the case of queen-right colony fusion, territorial defense benefits could outweigh fitness costs. We discuss the implications of our findings for ant colony cohesion and recognition systems.