THE ECOLOGY OF COMMUNAL BREEDING - THE CASE OF MULTIPLE-QUEEN LEPTOTHORACINE ANTS

Multiple-queen societies of ants are key subjects in the study of comm unal breeding. Societies of leptothoracine ants may be obligately mono gynous (contain a single reproductive queen), functionally monogynous (only one of several mated queens lays eggs), or facultatively polygyn ous (some colonies contain more than one egg-laying, mated queen). Thi s paper presents a framework for understanding these diverse social sy stems as a function of leptothoracine ecology. The framework is derive d from a synthesis of empirical information - in particular, a link be tween the social system and the degree of habitat patchiness - with th ree bodies of theory. These are ecological constraints theory, ESS (ev olutionarily stable strategy) models of dispersal, and kin selection m odels predicting the stable reproductive skew (allocation of reproduct ion). In contrast to several previous ecological hypotheses, multiple- queening in leptothoracines almost certainly results from high costs t o single queens of dispersal and colony foundation (high ecological co nstraints), which select for queens to seek adoption in their natal co lony. Factors raising these costs include nest-site limitation, cold c limate, and habitat patchiness. ESS models suggest that high dispersal costs lead to a larger stable fraction of non-dispersers and hence to higher relatedness between queens. Skew models predict that high ecol ogical constraints and high relatedness promote high skew (one or a fe w individuals dominate reproduction) and high within-colony aggression . Therefore, (i) extensive habitats with moderate costs of solitary co lony foundation should promote multiple-queening with high dispersal l evels, moderate queen relatedness, low reproductive skew, and low quee n aggression. By contrast, (ii) patchy habitats should induce multiple -queening with less dispersal, higher queen relatedness, higher skew, and higher aggression. In addition, (iii) habitats with small or widel y spaced nest-sites, or with low costs of founding colonies alone, sho uld lead to universal dispersal without multiple-queening. These assoc iations of traits occur in facultatively polygynous, functionally mono gynous and obligately monogynous leptothoracines respectively. Therefo re, the framework in this paper explains a substantial amount of the s ocial and ecological diversity of leptothoracine ants.