Dietary and taxonomic controls on incorporation of microbial carbon and phosphorus by detritivorous caddisflies
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Heterotrophic microbes on detritus play critical roles in the nutrition of detritivorous animals, yet few studies have examined factors controlling the acquisition of microbial nutrients toward detritivore growth, which is termed “incorporation". Here, we assessed effects of detrital substrate identity (leaf type), background nutrients, and detritivore species identity on detritivore incorporation of microbial carbon (C) and phosphorus (P) in leaf litter diets. We fed oak and maple litter conditioned under two nutrient concentrations (50 or 500 µg P L−1) to the detritivorous caddisfly larvae Ironoquia spp., Lepidostoma spp., and Pycnopsyche lepida and used the radioisotopes 14C as glucose and 33P as phosphate to dually trace incorporation of microbial C and P by caddisflies. Incorporation efficiencies of microbial C (mean ± SE = 12.3 ± 1.3 %) were one order of magnitude higher than gross growth efficiencies for bulk detrital C from recent studies (1.05 ± 0.08 %). Litter type did not affect incorporation of microbial nutrients; however, caddisflies incorporated microbial P 11 % less efficiently when fed litter from the higher P concentration. Two lower body C:P species (Pycnopsyche and Ironoquia) exhibited 9.9 and 7.1 % greater microbial C and 19.0 and 17.7 % greater microbial P incorporation efficiencies, respectively, than the higher body C:P species (Lepidostoma). Our findings support ecological stoichiometry theory on post-ingestive regulation that animals fed lower C:P diets should reduce P incorporation efficiency due to excess diet P or alleviation of P-limited growth, and that lower C:P species must incorporate dietary C and P more efficiently to support fast growth of P-rich tissues.
KeywordsDetritivores Leaf type Nutrient enrichment Ecological stoichiometry Radioisotopes
The National Science Foundation (DEB 1020722; BIO REU 1063067 and 1359188) and the University of Arkansas Honors College provided funding for this research. The authors would like to thank Brad Austin, Ayla Smartt, Kayla Sayre, Erin Scott, Erin Grantz, Jason Ramey, Delaney Hall, Amanda Eddy, Katharine Stewart, Andrew Sanders, Sally Entrekin, Chris Fuller, Dan Magoulick, Steve Beaupre, Duane Wolf, Ralph Henry, Julia Tchakhalian, and two anonymous reviewers for input and assistance. Halvor Halvorson was supported by a Doctoral Academy Fellowship at the University of Arkansas.
Author contribution statement
J. T. S. and M. A. E.-W. formulated the original idea; H. M. H. and M. A. E.-W. designed experiments; and H. M. H. and G. W. performed experiments and conducted statistical analysis. H. M. H. and M. A. E.-W. wrote the manuscript, and all authors provided editorial advice.
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