Predator-induced plastic changes in metabolomic profiles
The mechanisms underlying the widespread trait responses to predation risk are still poorly understood (Mitchell et al. 2017). Our results clearly showed predation risk changed the metabolome of the preyD. magna . One key finding was that the amino acid metabolism (i.e. valine, leucine and isoleucine biosynthesis, and metabolism of beta-alanine, arginine and proline, tryptophan and phenylalanine) was strongly affected across subpopulations under predation risk. The pronounced changes in amino acid metabolism indicates D. magna deals with predation risk by altering protein utilization. This complements a proteomic study showing that exposure to predator kairomones enhanced the biosynthetic activity of proteins in D. magna , particularly glyceraldehyde-3-phosphate dehydrogenase (GAPDH) that is necessary for biosynthesis of amino acids (Otte et al. 2014). Related to this, exposure to fish kairomones has been shown to upregulate genes involved in protein folding in D. magna (Schwarzenberger et al.2009). In addition, the predator-induced change in amino acid metabolism may partly reflect changes in stress protein levels as documented for the study species (Pauwels et al. 2005). Besides playing a central role in the metabolic turnover of proteins, amino acids are also used extensively in energy metabolism (Viant et al. 2003). The proteomic study indeed showed evidence for enhanced energy demand ofD. magna when under predation risk (Otte et al. 2014).