CS08 Biogeochemical Cycles
Date: Monday, June 10, 2002
Time: 2:15:00 PM
Location: Saanich
ElserJJ, Arizona State University, Tempe, USA, j.elser@asu.edu
Gorokhova, E, , University of Stockholm, Stockholm, Sweden, 
Dowling, T, A, Arizona State University, Tempe, USA, 
Weider, L, J, University of Oklahoma, Norman, USA, 
Crease, T, J, University of Guelph, Guelph, Canada, 
The genetic control of chemical factors in the environment: stoichiometric impacts and rDNA shifts in Daphnia under divergent selection on production rate
Variations of body C:N:P ratios in zooplankton affect trophic dynamics and nutrient recycling. It has been hypothesized that low C:P and N:P are associated with rapid growth rate due to its high demands for P-rich rRNA (the “growth rate hypothesis”, GRH). We tested the GRH by assessing juvenile growth rate and RNA and P contents in lineages subjected to divergent selection on weight-specific fecundity (WSF) and examining changes in ribosomal RNA genes (specifically, length of the intergenic spacer, IGS). Selection was imposed on offspring of a single progenitor female from an obligately parthenogenetic population of Daphnia pulex. WSF diverged rapidly, with significant reductions in WSF within two generations. Other changes accompanied shifts in WSF: juveniles produced by low-WSF females grew more rapidly and had higher RNA and P contents. An increased predominance of long IGS was observed in fast-growth, low-WSF lines. These results strongly support the GRH, indicate a genetic mechanism for the evolution of such associations, and demonstrate that Daphnia (and perhaps other parthenogens) possesses considerable potential for rapid adaptive change in major life history traits.