Male size dimorphism and alternative reproductive tactics in Formica exsecta ants (Hymenoptera, Formicidae)

Abstract

Formica exsecta Nyl. populations in southern Finland exhibit two distinct male size classes. This phenomenon, which also occurs in Formica sanguinea Latr., is seen both within single nests and at the population level. Small males (micraners) appear to mature later, to have sharper diurnal activity peaks and to disperse more widely than do large males (macraners). Micraners appear to predominate in crowded polydomous colonies characterized by strongly male biased sex ratios, while macraners are charac teristic of monodomous populations with a sex ratio close to 1:1. We suggest that macraners represent a mating tactic based on limited dispersal, including inbreeding, and that they may be most common during the early stage of the colony cycle preceding polygyny, while micraners represent an outbreeding strategy associated with a decline in resource availability.