Variation in C:N:P stoichiometry across a climate gradient in worker ants of the Aphaenogaster rudis species complex

Background/Question/Methods

Increasing numbers of studies have demonstrated intraspecific variation in elemental composition of organisms. However, relatively few studies have examined patterns of intraspecific variation in carbon (C), nitrogen (N), and phosphorus (P) in terrestrial insects across a large geographical scale, and to our knowledge, none have been done on social insects. Variation in elemental composition may be caused due to a variety of factors, including environmental conditions (e.g. temperature, precipitation, etc.), developmental stage, food availability and quality, among others. The exact causes and possible mechanisms which lead to this variation at large geographical scales is unclear. In this study, we investigated variation elemental composition in a temperate North American ant species complex, Aphaenogaster rudis. This species complex occurs across a large latitudinal gradient, and thus, experiences a wide range of climatic conditions and this may lead to variation in body elemental composition. Samples of ant pupae were collected along the eastern United States for total C, N, and P analysis. Whole ant colonies were also collected for a common garden experiment to determine whether any variation seen in elemental composition was due to some intrinsic properties of the ants or whether it may be due to local climate or resource conditions. 

Results/Conclusions

Our preliminary results show that ant pupal C, N, and P body content was unaffected by mean annual temperature (MAT) and mean annual precipitation (MAP). In contrast, an increase in either of the more variable climate predictors, diurnal range temperature (DRT) and annual precipitation seasonality (APS), resulted in an increase in C and decrease in N and P content in ant pupae. Ant pupal elemental composition appeared to generally vary with latitude but any variation in elemental composition seen between colonies disappeared when ant colonies were reared under the same conditions. These results suggest that increasing climate variability may shift ant pupal stoichiometry towards C storage. Understanding the physiological mechanisms underlying these patterns should provide important insight into deciphering whether and how climate change may affect the availability of these important macronutrients in animal consumers.