Figure 1. Construction costs of flagella in bacteria and eukaryotes as a function of cell volume.

Each point denotes a species. The costs are the sum over all flagella present on a single cell. (A) The absolute construction cost. The lines are power law fits to bacteria, eukaryotic flagellates (euglenids, kinetoplastids, and ‘other eukaryotes’), and ciliates and parabasalids. The equations are: ${\displaystyle c_{abs}=1.1\times {10}^9{V}^{0.81\pm 0.14}}$ , ${\displaystyle c_{abs}=2.6\times {10}^{10}{V}^{0.31\pm 0.03}}$ , and ${\displaystyle c_{abs}=2.8\times {10}^9{V}^{0.86\pm 0.10}}$ , respectively (exponent ± SE). (B) The construction costs of flagella relative to the construction costs of the entire cell. The line is a power law fit to the eukaryotic flagellates: $c_{rel}=0.98V^{-0.66\pm 0.03}$ . The grey-shaded triangle is explained in the Discussion. In both panels the asterisk marks Opalina ranarum, which resembles ciliates in its flagellar distribution but does not belong to the ciliate clade. Data in Figure 1—source data 1.

Figure 1—figure supplement 1. Overview of flagellar and cellular properties of eukaryotic species.

(A) Distribution of flagellum lengths for cells with less than eight flagella and cells with eight or more flagella. Only unique flagellar lengths for each species are included (also for B–E), otherwise ciliate and parabasalid data would overwhelm the plot. (B) Distribution of flagellum length for cells with or without a rod in their flagellum. (C) Flagellum length plotted against cell volume. The legend in Figure E holds for C–F. (D) Flagellum length plotted against number of flagella. (E) Number of flagella plotted against cell volume. (F) Cell aspect ratio plotted against cell volume. The aspect ratio is calculated by dividing the cell length by the cell width (or the geometric mean of the width and depth). The dashed line is a power law fit to all species: $1.57V^{0.052\pm 0.016}$ . Data in Figure 1—figure supplement 1—source data 1 and 2.

Figure 1—figure supplement 2. Relative flagellar construction costs of special cases plotted against cell volume.

The blue points show Anaeramoeba ignava, Anaeramoeba gargantua, Dinematomonas valida, and Psammosa pacifica, before correcting for their real flagellum shape. The red points show the same species after correction. The grey points represent other eukaryotic species, shown for comparison. Data in Figure 1—figure supplement 2—source data 1.