title: How do consumers deal with stoichiometric constraints? Lessons from functional genomics using Daphnia pulex.
abstract: Disaccord between the supply and demand of energy (carbon, C) and certain material elements (e.g. phosphorus, P) across trophic levels is common in most ecosystems and impacts the strength of trophic interactions and ecosystem functions such as productivity and nutrient recycling. Yet, we know little about mechanisms operating at the lower levels of biological organization that drive such higher-level ecological processes. Such information should help refine theories integrating biological processes at multiple levels of organization. Understanding the expression and functions of genes that underlie (to a large degree) physiological adjustments made by organisms to stoichiometric imbalances at trophic interfaces is a first step in this enterprise. Here, we investigate adjustments in gene expression to varying supply and demand of phosphorus relative to other dietary components in the keystone limnetic herbivore, Daphnia pulex. Daphniids were fed an algal diet of either LoC-HiP (molar C:P ∼100) or HiC-LoP (molar C:P ∼900) for 5 days, resulting in significant growth reductions under HiC-LoP conditions. Microarrays measured the transcriptional regulation of 8217 annotated protein-coding genes under contrasting dietary conditions and revealed 1818 differentially expressed (DE) genes; 19% are genes unique to the Daphnia lineage. We mapped DE genes onto a global chart of metabolic pathways to obtain a systems-level perspective on the responses to stoichiometric imbalances. Daphnia differentially regulated pathways were involved in sequestering limiting elements, and in dealing with the products of metabolic adjustments that may be triggered by nutrient stress in primary producers. Functional genomics at trophic interfaces illuminate the complexity of processes underlying stoichiometric constraints on energy and nutrient fluxes in ecosystems.
authors.affiliation: Department of Zoology, Oklahoma State University, Stillwater, OK 74078, USA. puni.jeyasingh@okstate.edu
authors.forename: Punidan D
authors.initials: PD
authors.lastname: Jeyasingh
authors.forename: Ashok
authors.initials: A
authors.lastname: Ragavendran
authors.forename: Susanne
authors.initials: S
authors.lastname: Paland
authors.forename: Jacqueline A
authors.initials: JA
authors.lastname: Lopez
authors.forename: Robert W
authors.initials: RW
authors.lastname: Sterner
authors.forename: John K
authors.initials: JK
authors.lastname: Colbourne
mesh_terms: D000818:Animals; D002244:Carbon / Q000378:metabolism; D003621:Daphnia / Q000235:genetics* / Q000254:growth & development; D020387:Food Chain; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D023281:Genomics / Q000379:methods*; D053858:Metabolic Networks and Pathways / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D010758:Phosphorus / Q000378:metabolism; D044444:Scenedesmus / Q000378:metabolism
chemical_list: D010758:Phosphorus; D002244:Carbon