4.5.2. Multivariate

Lipid trajectories were calculated using Principal Component Analysis (PCA). PCA allowed to track fatty acids changes in relative proportion in the whole fatty acid profile rather than in a given compound. The aim was to check whether fatty acid trajectories were convergent, divergent or alike in response to temperature increase. Trajectories were studied by comparing PCA scores (i.e., individuals) between host-algae and within each salinity treatment. PCA loadings (i.e., variables) was inspected visually to detect which fatty acids were responsible for lipid trajectories. Univariate staticitics were then performed as described above to validate any changes.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-3397/18/8/379/s1, Figure S1: *α* value as a function of salinity; Figure S2: Total fatty acid concentrations of *P. salina*.

**Author Contributions:** Conceptualization, S.P. and M.V.; Validation, C.H., T.M. and S.P.; Formal analysis, C.H.; Investigation, M.V., S.P., N.T.; Resources, M.V. and S.P.; Data curation, C.H.; Writing–original draft preparation, C.H.; Writing-review and editing, C.H., M.V., T.M., and S.P.; Visualization, C.H.; Supervision, S.P., C.H. and T.M.; Project administration, S.P. and C.H.; Funding acquisition, S.P. and C.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the French CNRS-INSU EC2CO program—project "ISLAY".

**Acknowledgments:** The authors thank the two anonymous reviewers for their constructive comments.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
