Genomic retention of both WASP and SCAR correctly predicts α-motility in the infectious chytrid fungus Bd. (A) Example chytrid zoospores with and without a flagellum migrating when confined between 1-µm spaced glass coverslips. See also Video 4. (B) Worm plots showing the tracks of 26 migrating chytrid zoospores with migration paths overlaid and with time 0 at (0,0). The endpoint of each cell’s path is shown with a dot. Only those cells obviously migrating were tracked, and cells were tracked for the duration of their movement. (C) Mean instantaneous speed of cells tracked in B. (D) Directional persistence (the ratio of the Euclidean distance to the accumulated distance) of cells tracked in B. Means and SD (bars) of the individual values (dots) combined from three biological replicates are shown.