Transcriptomic Response of Daphnia Magna to Nitrogen or Phosphorus Limited Diet

Abstract

Background: Effects of nutrient-imbalanced diet on the growth and fitness of zooplankton were widely reported. However, little is known about the molecular mechanisms driving the physiological changes of zooplankton under nutrient stress.Results: In this study, we investigated the physiological fitness and transcriptomic response of Daphnia magna when exposed to nitrogen (N)-limited or phosphorus (P)-limited algal diet (Chlamydomonas reinhardtii) compared to regular algae (N and P saturated). D. magna showed higher ingestion rates and over expression of genes encoding digestive enzymes when fed with either N-limited or P-limited algae, reflecting the compensatory feeding. Under P-limitation, both growth rate and reproduction rate of D. magna were greatly reduced, which could be attributed to the downregulated genes within the pathways of cell cycle and DNA replication. Growth rate of D. magna under N-limitation was similar to normal group, which could be explained by the high methylation level (by degradation of methionine) supporting the body development.Conclusions: Phenotypic changes of D. magna under nutrient stress were explained by gene and pathway regulations from transcriptome data. Generally, D. magna invested more on growth under N-limitation but kept maintenance (e.g. cell structure and defense to external stress) in priority under P-limitation. Post-translational modifications (e.g. methylation and protein folding) were important for D. magna to deal with nutrient constrains. This study reveals the fundamental mechanisms of zooplankton in dealing with elemental imbalanced diet and shed light on the transfer of energy and nutrient in aquatic ecosystems.