The value of oviposition timing, queen presence and kinship in a social insect

Reproductive cooperation confers benefits, but simultaneously creates conflicts among cooperators. Queens in multi-queen colonies of ants share a nest and its resources, but reproductive competition among queens often results in unequal reproduction. Two mutually non-exclusive factors may produce such inequality in reproduction: worker intervention or queen traits. Workers may intervene by favouring some queens over others, owing to either kinship or queen signals. Queens may differ in their intrinsic fecundity at the onset of oviposition or in their timing of the onset of oviposition, leading to their unequal representation in the brood. Here, we test the role of queen kin value (relatedness) to workers, timing of the onset of oviposition and signals of presence by queens in determining the maternity of offspring. We show that queens of the ant Formica fusca gained a significantly higher proportion of sexuals in the brood when ovipositing early, and that the presence of a caged queen resulted in a significant increase in both her share of sexual brood and her overall reproductive share. Moreover, the lower the kin value of the queen, the more the workers invested in their own reproduction by producing males. Our results show that both kinship and breeding phenology influence the outcome of reproductive conflicts, and the balance of direct and indirect fitness benefits in the multi-queen colonies of F. fusca.

繁殖合作虽可带来收益，但同时也会在合作者之间引发冲突。多蚁后蚁群中的蚁后共享巢穴与各类资源，但蚁后间的繁殖竞争往往会导致繁殖产出不均。有两类非互斥因素可造成此类繁殖不均：一是工蚁的干预行为，二是蚁后的自身性状。工蚁可通过偏爱部分蚁后而非其他个体实施干预，这种偏好可能源于亲缘关系或是蚁后释放的信号。蚁后在产卵初期的内在繁殖力，或是产卵起始时间上存在差异，这也会导致其在子代群体中的占比不均。本研究中，我们针对以下因素在子代母系归属判定中的作用展开检验：蚁后与工蚁的亲缘值（relatedness）、蚁后产卵起始时间，以及蚁后的存在信号。研究结果显示，产卵较早的丝光褐林蚁（Formica fusca）蚁后，其子代中有性生殖个体的占比显著更高；当笼中存在一只蚁后时，该蚁后的有性子代占比与整体繁殖占比均会显著提升。此外，蚁后与工蚁的亲缘值越低，工蚁就越倾向于通过生产雄性子代来投入自身繁殖。本研究结果表明，在F. fusca的多蚁后蚁群中，亲缘关系与繁殖物候（breeding phenology）均会影响繁殖冲突的结局，同时也会影响直接与间接适合度收益的平衡。