Evolutionarily diverse fungal zoospores show contrasting swimming patterns specific to ultrastructure

Zoosporic fungi, also called chytrids, produce motile spores with flagellar swimming tails (zoospores)1,2. These fungi are key components of aquatic food webs, acting as pathogens, saprotrophs and prey3-8. Little is known about the swimming behaviour of fungal zoospores, a crucial factor governing dispersal, biogeographical range, ecological function and infection dynamics6,9. Here, we track the swimming patterns of zoospores from 12 evolutionary divergent species of zoosporic fungi across seven orders of the Chytridiomycota and the Blastocladiomycota phyla. We report two major swimming patterns which correlate with the cytoskeletal ultrastructure of these zoospores. Specifically, we show that species without major cytoplasmic tubulin components swim in a circular fashion, while species that harbour prominent cytoplasmic tubulin structures swim in a pattern akin to a random walk (move-stop-redirect-move). We confirm cytoskeleton architecture by performing fluorescence confocal microscopy of the zoospores across all 12 species. We then treat representative species with variant swimming behaviours and cytoplasmic-cytoskeletal arrangements with tubulin stabilizing (Taxol) and depolymerizing (Nocodazole) pharmacological-compounds. We observed that when treating the random-walk species with Nocodazole their swimming behaviour changes to a circular swimming pattern. Confocal imaging of the nocodazole-treated zoospores demonstrates these cells maintain flagellum tubulin structures but lack their characteristic cytoplasmatic tubulin arrangement. These data confirm that the capability of zoospores to perform complex movements as a random walk is linked to the presence of prominent cytoplasmatic tubulin structures. We discuss the link between cytology, sensation, and swimming behaviour manifest in zoosporic fungi.