title: Dietary phosphate affects food selection, post-ingestive phosphorus fate, and performance of a polyphagous herbivore.
abstract: Comparisons of the carbon, nitrogen and phosphorus (P) content of plants and insect herbivores suggests that P limitation and herbivore foraging to balance P intake could be common. However, the lack of synthetic diets for testing the effects of lower ranges of dietary P has been a major impediment to experimental assessment of the ecological importance of, and physiological responses to, P limitation for terrestrial herbivores. We manipulated dietary P content (%P) over its observed range in terrestrial foliage using artificial diets containing near-optimal content of other nutrients for the grasshopper Schistocerca americana. Over much of the ecologically relevant range, when consuming single diets over a lifetime, higher P stimulated growth rates and increased survival, with an optimal dietary %P of 0.25-0.50% when measured throughout development. Excessive dietary P (1%) reduced growth and survival. However, with only short-term (3 day) confinement to single diets, dietary P had no effect on food consumption or growth rates. During these short exposures, fifth (but not third) instar hoppers increased the proportion of P excreted relative to P assimilated as dietary P increased. Target experiments demonstrated that, when given a choice, grasshoppers select among foods to attain a P intake target of 0.6%. These data suggest that P limitation could be common for terrestrial insect herbivores and that they can exhibit ingestive and post-ingestive mechanisms to attain sufficient but not excessive P.
authors.affiliation: School of Sustainability, Arizona State University, Tempe, AZ 85287, USA acease@asu.edu.
authors.forename: Arianne J
authors.initials: AJ
authors.lastname: Cease
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA Orange Coast College, Costa Mesa, CA 92626, USA.
authors.forename: Michelle
authors.initials: M
authors.lastname: Fay
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Elser
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
authors.forename: Jon F
authors.initials: JF
authors.lastname: Harrison
mesh_terms: D000818:Animals; D002755:Choice Behavior; D005243:Feces / Q000737:chemistry; D005260:Female; D005518:Food Preferences; D005526:Food, Formulated; D006110:Grasshoppers / Q000254:growth & development / Q000502:physiology*; D060434:Herbivory; D008297:Male; D010758:Phosphorus / Q000378:metabolism*
chemical_list: D010758:Phosphorus
keywords: Diet choice; Ecological stoichiometry; Geometric framework; Grasshopper; Phosphate; Synthetic diet