Original paper

Ontogenic differences in mayfly stoichiometry influence growth rates in response to phosphorus enrichment

Back, Jeffrey A.; Taylor, Jason M.; King, Ryan S.; Fallert, Kari L.; Hintzen, Emily H.

Abstract

We contrasted the carbon, nitrogen, and phosphorus (C : N : P) stoichiometry of Caenis spp. (Ephemeroptera:Caenidae) nymphs from 2 stream reaches differing in P enrichment. We also estimated growth rates of nymphs reared on algae of different P content across four development classes in a laboratory experiment. C : N ratios of field-collected nymphs exhibited variable responses across development classes between sites whereas C : P and N : P ratios showed a clear unimodal response, increasing from classes II through IV but then declining sharply in class V (nymphs nearing eclosion) at both sites. C : P was lower at the highly enriched site for all but the last development class. Growth rates increased in response to P enrichment at the earliest development class, but this growth response diminished in later development classes resulting in a significant interaction between P treatments and development classes. Trends in field data imply that later stages of development have higher P requirements than earlier classes and nutrient enrichment may affect sequestration of P by nymphs. Laboratory data suggest that early development classes are more P limited but in light of field results, nymphs may shift P allocation from somatic growth to reproductive development as organisms mature.

Keywords

c : n : p ratiosphosporus contentdevelopment classesgrowth ratesephemeropteracaenidae