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.

Figure 1.

Comparing variation in total body phosphorus content within and across taxa. (A) The intraspecific variation in Texas field crickets (Gryllus texensis; dark bars) is compared to the interspecific variation (across insect taxa - light bars) in total body phosphorus content; (B) The intraspecific variation in Cuculinoid weevils (Sabinia setosa; dark bars) is compared to the interspecific variation (across insect taxa - light bars) in total body phosphorus content. Interspecific variation data are from Woods et al. (2004).

Figure 2.

Comparing variation in total body nitrogen content within and across taxa. Intraspecific variation in Texas field crickets (Gryllus texensis; dark bars) is compared to the interspecific variation (across insect taxa - light bars) in total body nitrogen content. Interspecific variation data are from Fagan et al. (2004).