Access to Plant-based Carbohydrate Resources and Colony Investment for Two Ant Species

Bill D. Wills, Newton Hood, and Andrew V. Suarez
Department of Entomology, Michigan State University BDW; School of Integrative Biology, University of Illinois Urbana-Champaign NH; Department of Entomology, University of Illinois Urbana-Champaign AVS

Presented at the All Scientist Meeting (2015-04-15 to 2015-04-16 )

Body size represents a key life history trait that directly impacts an organism’s survival and reproductive success. In social insects, differential investment into worker size or worker number is thought to play an important role in determining colony success. Additionally, colony investment into worker size and number may shift in response to the availability of resources and associated reproductive tradeoffs (e.g., offspring size versus number). Access to carbohydrate-rich resources can influence colony establishment, growth, and the behavior. Moreover, colonies monopolizing carbohydrate-rich resources have been implicated in the ecological success of certain groups of ants. Here we conducted a diet manipulation experiment to test how access to carbohydrate resources affects colony investment in worker number, size (body mass), and morphology (head length, head width, hind tibia length, pronotal width) of an introduced, polymorphic ant species (Solenopsis invicta) and native, monomorphic ant species (Forelius pruinosus). Field collected colonies (n = 12) were divided into two equal size experimental subcolonies. Each experimental, colony was reared on a diet of insect protein, water, and one of two diet treatments (with and without access to carbohydrates). For both species, access to carbohydrate resources doubled worker biomass after 60 days. This increase in biomass resulted from shifts in worker number, but not necessarily shifts in worker body size. These changes in colony investment shed insight into how carbohydrate-rich resources can alter a colony’s worker force and in turn, may contribute to ecological success.

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