MULTIPLE QUEENS IN ANT NESTS - IMPACT ON GENETIC-STRUCTURE AND INCLUSIVE FITNESS

Polygyny, the occurrence of multiple laying queens in colonies of soci al insects, presents a potential challenge to our understanding of evo lution by kin selection. The ant species Leptothorax longispinosus is exceptionally useful for studying this problem, since populations vary in their frequency of polygyny and queen number had previously been l inked to ecological factors of density of nest sites and overwinter su rvival rate. In addition, colony structure is complex, with nests unde rgoing fissions, fusions, and worker exchanges. Here we investigate ge netic and spatial structure in three North American populations of thi s ant. Worker-worker relatedness remains high in these populations, pr imarily because queen-queen relatedness is likewise high; despite cons iderable genetic structure within nests, however, we found no evidence of spatiogenetic structure between nests. We conclude that the nest i s the functional unit of selection for these populations. Across nests , there appears to be consistent, strong, stabilizing selection for in termediate levels of polygyny in two northern populations. Variation i n queen number among populations and among nests within populations th us represents the outcome of a complex interplay between genetic and e cological factors.