Stridulatory organ morphology, acoustics, and function in the red imported fire ant

Abstract

The purpose of this research was to determine whether stridulation in the red imported fire ant (RIFA) serves a significant communicative function. Three general objectives were developed. 1) Characterize the stridulatory organ (SO). 2) Determine the information content of the signal through an acoustics analysis; and 3) Determine colony level employment of the SO. Characterization of the morphology of the SO revealed a general increase in all SO parameters (length, width, distance between teeth, and total teeth) in relation to ant size. This was most evident in the worker caste. The SO was significantly different between castes suggesting that the resulting acoustical properties could serve to distinguish each caste. Morphological analysis revealed that the SO of males is thin and unlikely to be very functional. Based on the differences in the structure of the SO between female castes, the possible evolution of the SO is discussed. Characterization of the acoustical properties, pulse length and pulse carrier frequency for both directions of gaster movement, showed that both were variable and overlapped between the female castes. This suggests that signals are not altered for different contexts (Markl et. al. 1977). Pulse lengths for both directions of gaster movement were the only properties shown to be significantly different between castes, while short pulse frequency was the only acoustical property found correlated to ant size. These differences are discussed in terms of selection, as opposed to allometric variation or developmental processes. Three colony level behaviors associated with RIFAs, disturbance response, emigration, and excavation, were examined for SO employment. Stridulation was not associated with mound disturbance or employed during nest emigration. However, stridulations were found to be significantly employed during soil excavation. Thus, sound may be serving one or more possible functions: 1) As an aid in the removal of soil particles; 2) As a signal communicating a need to dig; 3) As an acoustical imaging tool; and 4. As an aid in mound construction via particle compression and the expulsion of interstitial water.