Fig. 1.

Ecology of Cephalotes ants and origins of specimens used in our study. a Map showing sampling locales for cephalotines (Cephalotes and Procryptocerus) used in this study (stars), the activities they were used for, along with sample size (i.e., number of species). Numbered circles show sites of ant sampling in two prior studies^12,28, from which stable nitrogen isotope data were extracted and plotted here. The map was constructed using an open source geographic information system QGIS software version 2.18. b Nitrogen isotope data from prior studies^14,31 targeting several New World locales. Each separate box plot graphs the median (center line), the interquartile range (i.e., from the top to the bottom of each box), values equal to 1.5 times the interquartile range (tops and bottoms of whiskers), along with outliers. Graphed are isotope ratios for Cephalotes ants, other ants in their subfamily (Myrmicinae), and Camponotus ants, which host known N-recycling bacteria. Also plotted are data for plants, insect herbivores, and insect carnivores from the same locales. Isotope fractionation results in a gradual increase in the relative amounts of heavy nitrogen (¹⁵N), as one moves up the food chain. As such, ants with low amounts of the heavy nitrogen isotope, shown here using the δ¹⁵N statistic, are argued to feed at low trophic levels. c C. atratus workers tend honeydew-producing, ant-mimicking membracids (upper left, image credit: Jon Sanders). C. eduarduli and C. maculatus (smaller worker) feeding on bird droppings (lower left, from Fig. 2b of Russell et al.^16, used with permission from Myrmecological News and photographer Scott Powell). Soldier caste of C. varians with an outlined digestive tract (upper right, image credit: Corrie Moreau). A FISH microscopy image of a digestive tract from a Cephalotes worker is shown at lower right (image credit: Piotr Lukasik). Note the large bacterial mass in the ileum near the midgut–ileum junction, the site where N wastes are emptied via Malpighian tubules