Queen number, mode of colony founding, and queen reproductive success in ants (Hymenoptera Formicidae)

In ants, there are two main strategies of colony founding: young queens can start colonies without the help of workers (independent mode), or young queens need the help of workers (dependent mode). Independent founding is generally assumed to be the common manner of colony founding in ants, whereas dependent founding is thought to be a derived character typical of polygyne (i.e., several queens per colony) species with unicolonial nests. A comparative study of 24 European ant species showed that dependent colony founding is not restricted to unicolonial polygyne species but that a significant proportion of all polygyne species utilize this mode of reproduction. Twelve (92%) of 13 monogyne (i.e., a single queen per colony) species were independent founding species, and only one (8%) employed budding. In contrast, only three (27%) of the 11 polygyne species always used independent founding, two (18%) were either independent or dependent founding species, five (45%) of them employed only budding and one (9%) parasitic founding, suggesting that mode of colony founding may be associated with queen number per colony. Additionally, queen number per colony correlates with mode of colony founding in eight pairs (from seven different genera and four subfamilies) of closely related species (or forms) with contrasting modes of colony founding. In seven pairs, the independent founding species or form is monogyne, whereas its counterpart using budding is polygyne. In one additional pair, both forms are polygyne, but the form using dependent founding exhibits a higher degree of polygyny. Differences in the manner species start new colonies must influence the probability that newly-mated queens survive and successfully reproduce, and therefore the mode of reproduction should be considered when comparing reproductive success of queens across species. This is especially true since the present study shows that even closely related species can frequently differ in their mode of colony founding.