Extensive Natural Intraspecific Variation in Stoichiometric (C:N:P) Composition in Two Terrestrial Insect Species

Abstract

Heterotrophic organisms must obtain essential elements in sufficient quantities from their food. Because plants naturally exhibit extensive variation in their elemental content, it is important to quantify the within-species stoichiometric variation of consumers. If extensive stoichiometric variation exists, it may help explain consumer variation in life-history strategy and fitness. To date, however, research on stoichiometric variation has focused on interspecific differences and assumed minimal intraspecific differences. Here this assumption is tested. Natural variation is quantified in body stoichiometry of two terrestrial insects: the generalist field cricket, Gryllus texensis Cade and Otte (Orthoptera: Gryllidae) and a specialist curculionid weevil, Sabinia setosa (Le Conte) (Coleoptera: Curculionidae). Both species exhibited extensive intraspecific stoichiometric variation. Cricket body nitrogen content ranged from 8–12% and there was a four-fold difference in body phosphorus content, ranging from 0.32–1.27%. Body size explained half this stoichiometric variation, with larger individuals containing less nitrogen and phosphorus. Weevils exhibited an almost three-fold difference in body phosphorus content, ranging from 0.38–0.97%. Overall, the variation observed within each of these species is comparable to the variation previously observed across almost all terrestrial insect species.

Herbivore physiological response to predation risk and implications for ecosystem nutrient dynamics

“…Our work expands upon previous understanding (36,37) that the nutrient content of body tissue is not only constrained by dietary nutrient composition, but may vary with constraints imposed by internal physiological state in response to predation risk. Moreover, the magnitude of within-species variation in body elemental content is comparable to the magnitude across species variation observed in terrestrial insect species (31). Together, these insights suggest that body C:N within a species may be quite malleable, as opposed to being a fixed species property (5,8), thereby requiring reconsideration of how trophic transfer of material and energy between plants and herbivore is constrained.…”

“…This conclusion is drawn from observations of large mismatches in gross elemental C relative to N and P content between herbivore body tissue and plant resources, and the questionable assumption (31) that there is a homeostatic C:N ratio that does not depend on food-web structure. Our results suggest that this perspective gives an incomplete picture of herbivore-nutrient limitation because not all available C is in a nutritionally useable form (9,30) and that both nutrient requirements and body C:N can be variable between environmental conditions (31). Indeed, in our particular case, grasshoppers freely chose intake levels that exacerbated C ingestion and lead to heightened N release in feces.…”

Predator‐driven elemental cycling: the impact of predation and risk effects on ecosystem stoichiometry

“…This implies that C:N contents of herbivores are not fixed, for which there is emerging empirical support (Bertram et al. 2008; Persson et al. 2010).…”

The relationship between body mass and elemental composition in nymphs of the grasshopper Schistocerca americana

“…Previous studies have separately analyzed variation in nutrient storage (e.g., phosphorus storage and energy storage) (Sterner and Schwalbach 2001, Ventura and Catalan 2005, Sun et al 2013) and body size on the intraspecific variation in consumer stoichiometry (Hambäck et al 2009, El-Sabaawi et al 2012. Generally, in adult organisms for a given species, nitrogen (N) and phosphorus (P) concentrations, and N:P display inverse relationships with body mass (Elser et al 1996, Cross et al 2003, Woods et al 2004, Kay et al 2006, Bertram et al 2008, Schneider et al 2010. Nevertheless, few studies have explored the relationships among the body size, nutrient storage, and variation in consumer stoichiometry.…”