Application of CO₂ carbon stable isotope analysis to ant trophic ecology

Abstract

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 CO 2 is non-invasive and can provide useful ecological information because isotopic CO 2 signatures can reflect the diet and metabolism of an animal. However, this methodology has rarely been used on invertebrates and never on social insects. Here, we first tested whether this method reflects differences in δ 13 C-CO 2 between 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 after 24 h. Consequently, we used this technique on wild co-occurring ant species with different feeding preferences 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 ant Messor 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. scutellaris are generalists that rely on both C3 and C4 pathways, though with a preference for the former. Our results show that this methodology can be applied even to small animals such as ants and can provide useful information on the diets of generalist omnivores.

Sub-lethal doses of imidacloprid alter food selection in the invasive garden ant Lasius neglectus

“…The other most abundant ant species in the area is the Dolichoderinae Tapinoma sp. (T. nigerrimum group, Nylander, 1859), plus a few scattered colonies of the Myrmicinae species Crematogaster scutellaris (Oliver, 1972), Messor structor (Latreille, 1798), Messor capitatus (Latreille, 1798), Pheidole pallidula (Nylander, 1849), and the Formicinae species Camponotus aethiops (Latreille, 1798), and Plagiolepis pygmaea (Latreille, 1798) (see Balzani et al 2020). Workers of L. neglectus occupied the trunks of almost all the trees occurring in the area (mostly oaks, Quercus sp., but also cypresses, Cupressus spp., and pines, Pinus spp., Frizzi et al 2020).…”

CO2 scrubbing, zero gases, Keeling plots, and a mathematical approach to ameliorate the deleterious effects of ambient CO2 during 13C breath testing in humans and animals

“…Keeling plots provide one method to estimate the δ 13 CO 2 Exhaled of an animal where direct collection of pure breath samples is precluded 122–125 . They rely on the premise that the δ 13 CO 2 Bkg is known, and an animal is sealed inside an airtight container where VCO 2 continually increases the [CO 2 ] inside the container.…”

“…Keeling plots provide one method to estimate the δ 13 CO 2Exhaled of an animal where direct collection of pure breath samples is precluded. [122][123][124][125] They rely on the premise that the δ 13 CO 2Bkg is known, and an animal is sealed inside an airtight container where VCO 2 continually increases the [CO 2 ] inside the container. The researchers then periodically subsample (e.g., every few minutes) and measure the δ 13 CO 2Diluted of the series of the gas samples representing different mixtures of CO 2Bkg and CO 2Exhaled (Figure 3).…”