Nestmate recognition and population genetic structure in the Argentine ant, Linepithema humile.

Abstract

The Argentine ant, Linepithema humile, is a widespread invasive species characterized by reduced intraspecific aggression within its introduced range. To gain an understanding of mechanisms underlying nestmate recognition in the Argentine ant, I studied its population genetic structure and the role of genetic vs. environmental cues on aggression. I combine behavioral, genetic, and analytical data to explore the role of exogenous cues and recent changes in the population genetic structure on nestmate recognition in this ant. In Chapter II, I examined population genetic structure and intercolony aggression in two portions of the Argentine ant introduced range: California and the southeastern U.S. I describe factors that may have contributed to the present-day differences in genetic diversity between these two regions and I also suggest ecological factors that may have contributed to regional differences in current distribution patterns of the Argentine ant. In Chapter III, I examined the context-dependency of nestmate discrimination in the Argentine ant and the effect of action thresholds on exogenous cue recognition. I also tested hypotheses that explain a change in action thresholds as well as factors that affect action thresholds. I examined changes in intraspecific aggression in various discrimination contexts. I tested the importance of isolated nest referents on aggression thresholds. In Chapter IV, I examined the impact of different diet-derived hydrocarbons on intraspecific aggression in the Argentine ant and the potential of shared, diet-derived hydrocarbons to produce colony uniformity where intercolony genetic and/or environmental differences exist. In Chapter V, I examined the role of environmental cues on nestmate recognition in two populations of the Argentine ant. I tested the hypothesis that there is geographical variation in the response of Argentine ants to nestmate recognition cues derived from prey. In Appendix I, I use the Argentine ant to compare four aggression bioassays for consistency between replicates, similarity between assays, and ability to predict whole colony interactions. I tested four different aggression assays with two or three scoring methods per assay. I also determined whether isolated aggressive encounters could predict whole colony interactions.