Meeting Abstract
P2.128 Friday, Jan. 4 Interaction of Cooling Rate and Body Size on Cold Tolerance in the Red Imported Fire Ant (Solenopsis invicta) MARTIN, A.R.*; PORTER, S.D.; HAHN, D.A.; University of Florida; USDA CMAVE; University of Florida ardm@ufl.edu
Thermal stress can have profound effects on organismal performance, fecundity, and survival. Though many mechanisms are employed to cope with low-temperature stress, intrinsic characteristics of an individual as well as extrinsic environmental factors influence the net effect of cold exposure. Therefore, in order to develop an ecologically-relevant model of cold tolerance, both intrinsic and extrinsic factors must be considered. This experiment examined the effects of body size and cooling rate on the supercooling point and knockdown temperature of the red-imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Body size is a highly variable intrinsic factor that has been shown to affect stress resistance in many insect species. Cooling rate is an important extrinsic factor that may affect cold-tolerance. We hypothesized that cooling rate and body size will both have effects and may interact to set the supercooling point and knockdown temperature in fire ant workers. To observe the effects of cooling rate and body size on supercooling point, workers of a range of sizes were exposed to three cooling rates, a very fast ramp of -10°C/min, a slower ramp of -1°C/min, and an ecologically-relevant very slow ramp of -0.1°C/min. Knockdown temperature was examined using a similar method, though workers were exposed to only the two slowest cooling rates. Body size had a considerable effect on both supercooling point and knockdown temperature, with larger individuals freezing at higher temperatures and maintaining locomotion at lower temperatures than smaller individuals. Cooling rate had a very small effect on supercooling capacity and did not interact with body size. We are currently investigating the interactions between cooling rate and body size on knockdown temperature.
