Adaptive significance of early reproduction in Vespula shidai social wasps

Abstract

Organisms face the fundamental ecological question of when to switch resources from growth to reproduction or allocate resources between the two. Social wasps, including Vespula species (the yellowjackets), must crucially decide to transition from colony growth to reproductive production before the onset of winter. The timing of this transition could be influenced by worker numbers and environmental factors that affect the fitness of the colony. Early initiation of reproductive production has the advantage that a few reproductives can emerge if the colony collapses prematurely. In contrast, once reproductive production begins, nest growth terminates and the increase of future reproductives should be limited. This study investigated the group decision-making process regarding when and under what circumstances Vespula shidai initiates its reproductive phase. During the early reproductive period, we estimated the number of workers and new queens that emerged from the meconia in the cells. Significantly, a positive correlation was observed between the number of workers and the production of new queens during the early reproductive period. To examine the benefits of early reproduction, we reared V. shidai colonies in a plastic greenhouse, allowed males and new queens to fly and mate freely, and allowed the queens to begin overwintering at their timing. In our experimental environment, new queens that emerged earlier in the reproductive period had a higher survival rate during overwintering and higher dry and fat weights in the following spring. The higher dry and fat weights of the queens suggested better survival during the founding phase of the nest.