PARENT SESSION
Symposium #33: The ecology and evolution of coupled energy and material flows: integration of multiple scales and multiple biota.

Organized by: JD Schade, T Markow, and S Hobbie
Friday, August 9. 9:00 AM to 12:00 PM. Crystal Ballroom, TCC.

Elemental composition, growth rates, and rDNA structure in the genus Daphnia.

Weider, Lawrence^*,1, Glenn, Karen¹, Kyle, Marcia², Elser, James², ¹ University of Oklahoma, Norman, OK² University of Oklahoma, Norman, OK

ABSTRACT- Recent research has indicated that differences among organisms in C:N:P stoichiometry have major impacts on nutrient cycling and trophic dynamics in food webs. However, we do not yet fully understand the biological basis of differences in C:N:P ratios among organisms. Recent work (Elser et al. 2000.Ecology Letters 3:540-550) suggests that there should be an association between elemental composition (i.e. carbon, nitrogen, phosphorus - C:N:P ratios) of organisms and their food resources that will ultimately influence organismal growth rates. One proposed mechanism is that RNA:DNA levels, ribosomal DNA (rDNA) copy number, and rDNA intergenic spacer (IGS) lengths will be positively correlated with organismal phosphorus (P) concentrations because nucleic acids (RNA, DNA) are P-rich compounds. In addition, increased RNA levels, increased copy number, and longer rDNA IGS regions should be positively correlated with specific growth rate due to the hypothesized close association between the number of sites for transcription in rDNA motifs, and the increased potential for more rapid protein synthesis leading to higher growth rates. We examined the relationships between elemental composition (C:N:P), RNA:DNA ratios, rDNA IGS length variation, and growth rates in the microcrustacean zooplankter, genus Daphnia. We compare and contrast both interspecific and intraspecific variation, and relate these findings to the ecology and evolution of members of this genus. Results from this work may help provide a framework that couples sub-organismal processes with processes operating at higher levels (i.e. organism, population, community, ecosystem).

KEY WORDS: stoichiometry, rDNA, growth, cladocerans