Results
General metabolomic
responses
We used mass spectrometry-based metabolomics to explore the metabolomes
of D. magna . We obtained 2152 metabolites for the positive ion
mode and 1519 metabolites for the negative ion mode. A PCA showed that
fish kairomones induced a clear separation of the metabolomes along PC2
(Figure 1a, b). While there was also a separation along PC1, this was
not linked to the treatments or clonal differences (see details in
Supplementary Information). A two-way ANOVA on the PC2 scores showed
significant effects of the fish kairomone treatment and the fish
kairomone × subpopulation interaction (all P < 0.001,
Table S1). These significant effects were confirmed by the ASCA model
results (all P < 0.0001, see details in Supplementary
Information). Because of the
significant fish kairomone × subpopulation effect, we conducted separate
PLS-DA for each subpopulation, and found the fish kairomone treatment
significantly changed the metabolomes in each subpopulation (allP < 0.001, Figure 1c-h, Table S2).
Using MetaboAnalyst we found that four metabolic pathways for the
positive ion mode and five pathways for the negative ion mode were
affected by fish kairomones, these were mostly linked to amino acid and
sugar metabolism (Figure 2).