Latitudinal Gradients, Natural Selection, and Variation in N:P Stoichiometry in Plankton: A Test of the Growth Rate Hypothesis

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Elser 9527322 How does elemental composition ("stoichiometry") of animals vary among species? How might differences in body elemental composition affect how food webs function? This project will test the hypothesis that differences among species in body stoichiometry of the nutrients nitrogen (N) and phosphorus (P) reflect differences among species in specific growth rate. It is predicted that rapidly growing organisms must have high ribosome concentrations in their bodies. Ribosomes are P-rich (low N:P) cellular structures responsible for protein synthesis and thus growth. Therefore, rapidly growing organisms are predicted to have lower N:P ratios in their bodies that slower growing species. We will test this hypothesis by studying elemental and biochemical composition and body growth rates of zooplankton species at high latitudes vs. mid-latitudes. Natural selection along latitudinal gradients is hypothesized to select for differing growth rates among similar planktonic species. We will study ecological and evolutionary determinants of a parameter, animal N:P stoichiometry, that is likely to be a key factor influencing food webs of lake and ocean ecosystems.