Evolutionarily diverse fungal zoospores show contrasting swimming patterns specific to ultrastructure

Abstract

Zoosporic fungi produce unicellular motile reproductive spores with swimming tails (zoospores). These fungi are key components of aquatic food webs, acting as parasites, saprotrophs and prey, with some species representing ecologically important infectious diseases (e.g., of amphibian hosts). However, little is known about the swimming behaviour of fungal zoospores, a crucial factor governing dispersal in aquatic environments and therefore the ecological function of these fungi. Here, we track the swimming patterns of zoospores representing six species from two different phyla: Chytridiomycota and Blastocladiomycota. We report phylum-specific patterns in which Chytridiomycota species swim in a circular fashion, while Blastocladiomycota species swim in a pattern more akin to a random walk (move-stop-redirect-move). Additionally, we performed fluorescence confocal analyses of zoospores for all six species confirming they possess variant phylum-specific zoospore ultrastructures, specifically the distribution of the main cytoskeletal proteins and the number and arrangement of lipid droplet organelles within the cell. Lastly, we hypothesize a possible link between cytology, sensing of environment and swimming behaviour for these zoosporic fungi. We suggest that comparative study of these two groups will enable new understanding of the relationship between ultrastructure, cellular proteome, and how single celled eukaryotes direct flagellum-based movement.