Submitted by Neil Tsutsui on
Argentine ants (Linepithema humile) are globally widespread invasive ants that form colonies of billions of individuals without clear boundaries between nest sites. These “supercolonies” have very low aggression between colony members, which keeps intracolonial mortality low. However, there is very high aggression between different colonies. These ants use their antennae to smell the cuticles of other ants to determine whether they are from their own or a different colony. This odor is due to Cuticular HydroCarbons (CHCs), a waxy substance that covers their entire body. The colony-specificity of this odor is encoded by different length CHCs as well as modifications to these hydrocarbon chains (double bonds, methyl-group additions). CHCs are commonly found on most insects, where their main role appears to be the prevention of desiccation by forming a physical barrier to water evaporation. Straight-chain CHCs (i.e. no double-bonds or modifications) may be better at preventing desiccation due to tighter packing of the chains on the cuticle, but they are less useful for communication (i.e. odor differences) because there is less variability to give a colony cue. We have populations of Argentine ants across California that differ in their environments (e.g. temperature, humidity, precipitation), and this may provide differing selective pressures for desiccation resistance. With this research, I want to answer the question: “What are the differences in CHC-based desiccation resistance relative to differences in environment and colony behavior?”
The Tsutsui lab has a long history of researching the dynamics of the Argentine ant society and this project aims to expand that expertise into the effects of CHC variation on desiccation resistance and communication. We have existing data on ant survival at different humidity levels. This project aims to expand that knowledge into an understanding of how the composition of the CHC profile affects this resistance. The main method employed in this project will be assessing the melting temperature of CHC blends, as well as individual components. Using this method, we can determine how different blends of hydrocarbons alter the overall blend’s melting temperature, and therefore can ascertain which blends are most likely to resist desiccation. Gas chromatography and mass spectrometry will also be used to identify compounds in the CHC blend.
Field work = travel to field collection sites in the Bay Area, develop search image of Argentine ant nest sites, collect ants, and learn basic ant biology
Lab work = care for ants (feeding, watering and cleaning nests), hexane extraction techniques to collect CHCs, melting temperature assessment using Melting Point Apparatus, Gas Chromatograph-Mass Spectrometry and subsequent data analysis
Independent, enthusiastic, and experienced. Good experiences include field work, rearing of insects, and/or lab work with DNA analysis, however this project is most beneficial for a student deeply interested in animal behavior and/or social insect biology.