THE ECOLOGY OF COOPERATION IN WASPS - CAUSES AND CONSEQUENCES OF ALTERNATIVE REPRODUCTIVE DECISIONS

Polistes wasps can initiate colonies by themselves, but spring foundre sses often cooperate in constructing a shared nest and raising a commo n brood. The relative benefits for such cooperation vary across enviro nmental and social contexts and thus foundresses should shift reproduc tive strategies when contexts change. An experimental study of 10 fiel d populations of P. dominulus provides evidence for such strategy shif ts. P. dominulus females displayed three basic alternative reproductiv e strategies: initiate a nest alone or as a dominant on a multifoundre ss nest, join as a subordinate, or refrain from nesting and instead '' sit-and-wait'' for reproductive opportunities to open later in the sea son. In our populations, joining likely yields inclusive fitness benef its by increasing colony survival and resistance to usurpation. Nevert heless, joiners and other foundresses readily moved to improve their s ituations by (1) adopting orphaned nests. (2) switching to larger nest s, and (3) usurping small nests, which may have had a weakened foundre ss or a foundress with relatively low motivation for nest defense. Joi ning occurring more often early in the season, and adopting and usurpi ng occurring more often later were consistent with inclusive fitness m aximization. Lost past investments in nests did not affect future deci sions. Overall, residents of nests were larger than the wasps that joi ned them, but this difference decreased over the course of the season. Wasps that had cooperated in the past to form multifoundress associat ions were more likely to renest (usually together) after removal of th eir original nest than were single foundresses. After nest loss, singl e foundresses were more likely than multiple foundresses to take over another wasp's nest by adoption or usurpation. Cooperation within mult ifoundress associations is facultative and the balance between coopera tion and conflict theoretically depends on the asymmetry in reproducti on resulting from the asymmetry in dominance. P. dominulus cofoundress es closer in size (less asymmetrical in dominance) added cells to thei r nests more slowly and produced significantly smaller nests and fewer workers than associations with more size variation, as would be predi cted by greater conflict between wasps that are closer in size. The de cline in size differences between joining wasps and residents suggests that late-season joiners were relatively large wasps seeking to domin ate residents. Conflict on the nest may also explain why multiple foun dresses disappeared from nests at a higher rate than did single foundr esses. In sum, the multiple reproductive options of P. dominulus lead to a dynamic and flexible balance between cooperation and conflict in their social interactions.