Axioscope 7 microscope

Differential interference contrast (DIC) imaging was done for all replicates from the table with an Olympus BX-60 microscope (Olympus, Japan) with a ProgRes C14plus camera and the ProgRes CapturePro Software (version 2.9.01) (JENOPTIK AG). The morphology of chosen conditions (Fig. 1, Extended Data Figs. 4–6 and Supplementary Fig. 1) of Mesotaenium cells that were 89 h on the table was analysed.
For algae that were used for quantifying the abundance of LD per cell, a ZEISS Axioscope 7 microscope (Carl Zeiss) was used including the Zen software (Carl Zeiss). The LD count was carried out in Fiji^{159 (link)}. For statistical analysis of the LD count data, we first used a Shapiro–Wilk test^{160 (link)} to assess normality and used Mann–Whitney U tests^{161 (link)} with R (version 3.6.1) accordingly.
Confocal laser scanning microscope was done on a Zeiss LSM780 (Carl Zeiss) set as in Müller et al.^{162 (link)}. For the staining of the LD structures, we used the neutral lipid specific stain BODIPY 493/503 (EM/EX) (Merck). Mesotaenium cells were grown for 22 days on WHM medium at 70–80 µmol photons m⁻² s⁻¹ and 22 °C. These cells were ultrasonicated for 1 min with 1:500 BODIPY and incubated on a shaker for 5 min before visualization.

Images were acquired at 40× using a Zeiss Axioscope 7 microscope (Carl Zeiss Canada Ltd., Toronto, ON, Canada. Neurons were considered positive if there was fluorescently labelled antibody within cell bodies or processes, which were demarcated with tubulin. At least 100 neurons were analyzed per treatment and each experiment was repeated at least three times.