Application of CO2 carbon stable isotope analysis to ant trophic ecology

Stable isotope analysis of animal tissues is commonly used to infer diet and trophic position. However, it requires destructive sampling. The analysis of carbon isotopes from exhaled CO2 is non-invasive and can provide useful ecological information because isotopic CO2 signatures can reflect thediet and metabolism of an animal. However, this methodology has rarely been used on invertebratesand never on social insects. Here, we first tested whether this method reflects differences in delta 13C-CO2between workers of the Mediterranean ant Crematogaster scutellaris (Olivier) (Hymenoptera: Formicidae, Crematogastrini) fed with sugar from beet (C3; Beta vulgaris L., Amaranthaceae) or cane (C4;Saccharum officinarum L., Poaceae). We found that a significant difference can be obtained after24 h. Consequently, we used this technique on wild co-occurring ant species with different feedingpreferences to assess their reliance on C3 or C4 sources. For this purpose, we sampled workers of C.scutellaris, the invasive garden ant Lasius neglectus (van Loon et al.) (Lasiini), and the harvester antMessor capitatus (Latreille) (Stenammini). No significant differences in their carbon isotopic signatures were recorded, suggesting that in our study site no niche partitioning occurs based on the carbon pathway, with all species sharing similar resources. However, further analysis revealed that M.capitatus, a seed-eating ant, can be regarded as a C3 specialist, whereas L. neglectus and C. scutellarisare generalists that rely on both C3 and C4 pathways, though with a preference for the former. Ourresults show that this methodology can be applied even to small animals such as ants and can provideuseful information on the diets of generalist omnivores.