Meeting Abstract
31.5 Wednesday, Jan. 5 Worker size effects on the tunneling performance of the red imported fire ant GRAVISH, N*; GARCIA, M; UMBANHOWAR, P.B.; GOODISMAN, M.A.D.; GOLDMAN, D.I.; Georgia Tech; Georgia Tech; Northwestern University; Georgia Tech; Georgia Tech nick.gravish@gmail.com
Colonies of the red imported fire ant, Solenopsis invicta, are polymorphic (consist of a range of sizes) and members work together to construct large subterranean nests in soil. In a range of soil types, nests consist of vertical tunnels connecting hundreds of subterranean galleries. Although nest morphology has been carefully studied at the macro-scale, there have been far fewer studies of the tunneling process at the level of the individual. S. invicta body length can vary by a factor of 2.5 between the largest and smallest workers and jaw width varies similarly implying that the large workers at minimum should be able to carry 2.5 times the amount of grains in their jaws compared to smaller workers; thus we hypothesize that worker size (body width; w) should positively influence tunneling performance. To test this hypothesis, we studied the digging of equal numbers of S. invicta segregated into three treatments, small (w<0.7mm), large (w>1.0 mm), and a control mimicking the colonies natural distribution. Ants were confined to a large quasi-2D container filled with a simulated soil of wetted glass beads (diameter 0.25mm) and allowed to dig for 3 days. Nest volume was not significantly different between large and small workers (p=0.35) however significant differences in the length (p<0.05) and width (p<0.05) of tunnels were observed. Large workers tended to dig wider tunnels (3.3±0.6 mm) at the expense of shorter length while the small workers created narrower tunnels (2.6±0.6 mm) with longer total length. We conclude that worker size does not limit digging rate but does influence tunnel morphology. Control groups outperformed all treatments in nest volume suggesting that behavioral roles strongly influence digging rate.
