Abstract
Parasitism is certainly one of the most important driving biotic factors of cyanobacterial blooms which remains largely understudied. Among these parasites, fungi from the phylum Chytridiomycota (i.e. chytrids) are the only eukaryotic microorganisms infecting cyanobacteria. Here, we address spatiotemporal dynamics of the cyanobacterial host Dolichospermum macrosporum (syn. Anabaena macrospora) and its associated chytrid parasites, Rhizosiphon spp., in an eutrophic lake by studying spatial (vertical, horizontal) and temporal (annual and inter-annual) variations. Our results show homogenous chytrid infection patterns along the water column and across sampling stations. However, the prevalence of infection presented drastic changes with time, at both intra- and inter-annual scales. In 2007, a maximum of 98% of vegetative cells were infected by R. crassum whereas this fungal species was not reported seven years later. In opposite, R. akinetum, a chytrid infecting only akinetes, increased its prevalence by 42% during the same period. High chytrid infection rate on the akinetes might have sizeable consequences on host recruitment (and proliferation) success from year to year, as supported by the recorded inter-annual host dynamics (affecting also the success of other chytrid parasites). The spatial homogenous chytrid infection on this cyanobacterium, coupled to both seasonal and inter-annual changes indicates that time, rather than space, controls such highly dynamic host-parasite relationships.
Highlights
Parasitism is certainly one of the most important driving biotic factors of cyanobacterial blooms which remains largely understudied
Parasitic chytrids are totally dependent on specific hosts, to the best of our knowledge, only a single study dealt with the spatiotemporal dynamics of particular chytrid-phytoplankton pairings[20]
The cyanobacterial host community was exclusively composed of D. macrosporum, which largely dominated the phytoplankton community, accounting up to 87.41 ± 0.02% of the phytoplanktonic cells on Oct. 14th
Summary
Parasitism is certainly one of the most important driving biotic factors of cyanobacterial blooms which remains largely understudied Among these parasites, fungi from the phylum Chytridiomycota (i.e. chytrids) are the only eukaryotic microorganisms infecting cyanobacteria. Anabaena macrospora) and its chytrid parasites Rhizosiphon crassum and R. akinetum, at two contrasted stations (a deep central station (CS) and a shallow littoral station (LS) (Supplementary Fig. 1)), within the eutrophic Lake Aydat during the D. macrosporum cyanobacterial bloom in 2011. We analyzed both host and parasite populations by investigating host densities, the prevalence and the intensity of chytrid infection, the different stages of chytrid life cycles, as well as chytrid fecundity. Changes in parasitic species observed across these 7 years suggest that beyond the commonly reported direct effect of chytrid parasitism on the decline of cyanobacterial bloom, chytrids affect cyanobacterial bloom from year to year by infecting the resting cells
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