Helping effort and future tness in cooperative animal societies

Little attention has been paid to a conspicuous and universal feature of animal societies: the variation between individuals in helping e¡ort. Here, we develop a multiplayer kin-selection model that assumes that subordinates face a trade-o ¡ because current investment in help reduces their own future reproduc-tive success. The model makes two predictions: (i) subordinates will work less hard the closer they are to inheriting breeding status; and (ii) for a given dominance rank, subordinates will work less hard in larger groups. The second prediction re£ects the larger pay-o ¡ from inheriting a larger group. Both predictions were tested through a ¢eld experiment on the paper wasp Polistes dominulus. First, we measured an index of helping e¡ort among subordinates, then we removed successive dominants to reveal the inheritance ranks of the subordinates: their positions in the queue to inherit dominance.We found that both inheri-tance rank and group size had signi¢cant e¡ects on helping e¡ort, in the manner predicted by our model. The close match between our theoretical and empirical results suggests that individuals adjust their helping e¡ort according to their expected future reproductive success. This relationship has probably remained hidden in previous studies that have focused on variation in genetic relatedness