Species-level variation of Capniid winter stonefly (Allocapnia spp.) elemental composition

Background/Question/Methods

Species-level variation in the elemental composition of benthic macroinvertebrate genera is not well known in part because many taxa can only be identified to species level in the terrestrial adult stage, like Capniidae winter stoneflies. These species are morphologically similar except for reproductive anatomy, although body size can vary across species and between the sexes. Little is known about intra-specific variation in other life history traits, like growth rate, that are known to drive organismal elemental composition differences. We collected adult winter stoneflies (Allocapnia spp.) from 10 streams distributed across four ecoregions of Arkansas [Ozark Highlands (OH), Boston Mountains, Arkansas Valley, and Ouachita Mountains] during the winter of 2020-2022. Adults were identified and total body length measured. Then, individuals were dried and analyzed for carbon (C), nitrogen (N), and phosphorus (P).

Results/Conclusions

The percent C, N, and P of A. rickeri and mohri collected from OH streams were similar and did not differ by sex (mean+1SE=47.3+0.6, 10.8+0.1, 0.81+0.04). Further, the molar C:N of these two common species did not differ (5.1+0.1, p=0.89). Regression on all individuals suggested that body length was positively related to %C (R2=0.49, p=0.004), but not to %N (p=0.11) or C:N (p=0.14). Winter stoneflies are important stream detritivores that are sensitive to water quality; data on the species-level variation body stoichiometry should improve our understanding of the ecological stoichiometry of brown food webs and detritivore species responses to nutrient enrichment.