Rules for Allocation in a Temperate Forest Ant: Demography, Natural Selection, and Queen-Worker Conflict

The division of resources between growth and reproduction is a fundamental decision in the life history of an organism. I have quantified the division of resources between growth and reproduction for two populations of the temperate forest ant Leptothorax longispinosus over 3 yr. There was a significant annual and population variation in the amount of growth and reproduction made by nests. Protein supplementation caused each of these to increase compared to site- and year-matched control nests. The pattern of allocation, however, was unaffected by either site or food treatment. Path analysis showed that nest demography was a major factor controlling allocation patterns in this species. Other rules were also deduced, but nests from the two populations differed in how these rules were applied. Growth was consistently more important to total output than reproduction in Vermont nests, while nests from New York were more flexible. The allocation pattern shown by nests from Vermont was best explained by a model that emphasized natural selection acting at a proximate level, while the allocation pattern used by New York nests was best explained if selection was acting on ultimate-level processes. Nests in the two populations showed differences in the presence of queen-worker conflict over sexual allocation and reproductive allocation. These population differences may arise because nests in Vermont face tighter ecological constraints than nests in New York, especially with respect to nest site limitation.