Elsevier

Animal Behaviour

Volume 76, Issue 5, November 2008, Pages 1727-1733
Animal Behaviour

Near-infrared spectroscopy as a tool in behavioural ecology: a case study of the weaver ant, Oecophylla smaragdina

https://doi.org/10.1016/j.anbehav.2008.07.025Get rights and content

Cuticular hydrocarbons (CHCs) play an important role in insect recognition systems. A growing body of evidence indicates that insects are able to act upon the information contained in CHCs. However, investigating the behavioural response of insects to cuticular compounds usually involves the extraction and analysis of CHCs using gas chromatography–mass spectroscopy, which is a time-consuming and expensive process. Near-infrared spectroscopy (NIRS) may provide a much faster and less expensive technique for studying the behavioural response of insects to cuticular compounds. Here we present a case study of intercolonial aggression in the weaver ant, Oecophylla smaragdina. The differences between colonies detected by NIRS were reflected in the behaviour of colony members. The level of aggression expressed by colonies towards intruders increased as the spectral distance between colonies increased. The variability in the aggressive response also increased as the breadth of within-colony variation in spectra increased. This demonstrates that spectra generated using NIRS contain information to which weaver ants are able to respond. We discuss the implications of this for behavioural studies that have previously depended upon the extraction and analysis of CHCs.

Section snippets

Methods

We collected 120 weaver ants from each of six colonies in the grounds of James Cook University, Cairns, North Queensland (16°49′S, 145°41′E). None of the colonies were near neighbours. We stored samples at −4 °C before thawing and scanning with a Bruker Optics Multi Purpose Analyzer.

Results

The mean level of aggression displayed by recipient colonies towards colonymates was very low (A = 0.07; 95% confidence interval [CI]: 0.01–0.15), and rarely consisted of more than occasional aggressive posturing. The level of aggression displayed towards individual intruders from other colonies was highly variable, resulting in large confidence intervals around the means. The aggression index A ranged from 4.80 (CI: 2.53–7.53) for Colony 2 to 18.10 (CI: 13.68–22.56) for Colony 4.

Aggression

Discussion

The CHCs of the insect cuticle contain a large quantity of information to which individual insects can potentially respond. That they do so has been demonstrated across a range of taxa in a variety of contexts. Among social insects, aggression between colonies has been found to increase with chemical distance in several taxa. In the present study, we demonstrated that spectra generated using NIRS also contain or are correlated with information to which weaver ants were able to respond. The

Acknowledgments

We thank the Department of Primary Industries and Fisheries (Queensland Government) and the Rapid Assessment Unit of James Cook University Cairns for making the equipment available for this study. This work was supported by funds from James Cook University and the Australian Research Council (DP0665890 to R.H.C.), and P.N. is supported by a James Cook University fellowship. We also thank two anonymous referees for helpful comments and suggestions on the manuscript.

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    S. K. A. Robson and R. H. Crozier are at the School of Marine and Tropical Biology, James Cook University, Townsville QLD 4811, Australia.

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