The plasticity of life history traits depends on both environmental and genetic factors.  It is important to consider the effects of genotypic variability, especially in non-neutral markers, on life history traits in ecological interactions.  We address the interaction of environmental factors (resource availability and predation) and genetic factors (interclonal variation in intergenic spacer (IGS) length) in a laboratory experiment measuring life histories of unique Daphnia IGS clones in response to different combinations of food qualities and predator cues.  IGS length variation has the potential to limit the scope of Daphnia life history.  This region is critical to protein synthesis – and therefore growth and development – because each IGS subrepeat contains regulatory elements central to ribosomal RNA transcription and ribosome production.  We reared three Daphnia clones from birth to release of fifth clutch in P-sufficient (algae C:P 150) or P-deficient conditions (algae C:P 750), and exposed them to four predator kairomone treatments (no predator, Chaoborus, fish, and fish+Chaoborus) to determine whether Daphnia life history response differs for clones displaying shorter and longer IGS length variants.  We also measured the interaction of resource quality, predation, and IGS length, and its effects on Daphnia life history.
Results/Conclusions

We identified significant effects of clone – chosen based on IGS length – on life history in the presence of different resource qualities and different predator kairomones.  Similarly, predator cues – in the form of Chaoborus and fish kairomones – had a significant effect on Daphnia life history regardless of resource availability and IGS genotype.  In contrast, P-availability mediated plasticity in life history traits to differing degrees depending on genotype (clone) and environment (predator).  Because parthenogenetic species like Daphnia possess considerable flexibility to adapt via structural mutations in rDNA, predation has the potential to affect not just life history but also IGS length and copy number, and resource availability has the potential to mediate genotypic response and phenotypic plasticity.