Meeting Abstract
P3.43 Monday, Jan. 6 15:30 Dietary phosphate strongly and nonlinearly affects performance of an omnivourous herbivore CEASE, A.J.*; FAY, M.; ELSER, J.J.; HARRISON, J.F.; The University of Sydney; Arizona State University; Arizona State University; Arizona State University arianne.cease@sydney.edu.au
Comparison of the nitrogen, carbohydrate and phosphorus contents of plants and herbivores suggest that phosphorus (P) limitation should be common in herbivores; however, the effect of dietary P on the performance of most clades of herbivores has received little attention. We examined the effect of dietary %P in the context of artificial diets containing near-optimal contents of other nutrients on the growth, development and survival of the polyphagous grasshopper Schistocerca americana. Dietary phosphate levels had a nonlinear effect. Over the range of % P found in 90% of terrestrial foliage, higher P stimulated growth rates and increased survival, with an optimal dietary %P of roughly 0.5%. Higher P levels reduced growth and survival. We then tested grasshoppers for three days during either the third or final juvenile instars (rather than throughout development). During the three-day period, grasshoppers from all dietary %P treatment groups ate similar amounts of food, but grasshoppers eating low-P diets selectively absorbed more and excreted less P than high-P diets. Third instar nymphs assimilated more P on high P diets than final instar nymphs, which had high P excretion rates. Target experiments in which grasshoppers were provided with pairs of diets low and high in P demonstrated that grasshoppers select among foods to attain a P intake target of 0.6% P. Despite the clear importance of P to performance of grasshoppers confined to artificial diets, P may be less important in field contexts as the requirement for P is quantitatively much less than for carbohydrate or protein; thus selective feeding on a few P-rich leaves may enable grasshoppers to overcome low P levels in most of the foliage. In contrast, P-limitation seems more likely for herbivores with reduced mobility or host diversity.
