Department of Ecology and Evolutionary Biology, University of Michigan, 1105 North University Ave, Ann Arbor, MI 48109-1085, USA; Great Lakes Institute for Environmental Research (GLIER), University of Windsor, 401 Sunset Ave., Windsor, Ontario, Canada N9B 3P4; Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403, USA.
Great Lakes Institute for Environmental Research (GLIER), University of Windsor, 401 Sunset Ave., Windsor, Ontario, Canada N9B 3P4.
Harmful Algae. 2023 Feb;122:102381. doi: 10.1016/j.hal.2023.102381. Epub 2023 Jan 12.
Cyanobacteria have a great diversity of natural enemies, such as herbivores and pathogens, including fungal pathogens within the Chytridiomycota (chytrids). While these pathogens have been previously described on a select number of cyanobacterial hosts and are suspected to play a significant ecological role, little is understood about species interactions and how competition between parasites can affect epidemic development and bloom formation. Here, three Planktothrix agardhii isolates from Sandusky Bay, Lake Erie (OH, USA) were challenged in monoculture and polyculture against infection by three isolates (C1, C2, C10) of their obligate chytrid fungal pathogen, Rhizophydiales sp. The chytrid isolates were inoculated as single isolates or a mixture of up to three different isolates. In monoculture, host isolates were characterized as highly susceptible (P. agardhii 1030), moderately susceptible (P. agardhii 1808) or mostly resistant (P. agardhii 1801). Co-infection of chytrid isolates on the highly susceptible host isolate had an additive effect on chytrid prevalence, leading to a culture crash where 2 or 3 chytrid isolates were present. Co-infection of chytrid isolates on the moderately susceptible and mostly resistant isolates had no effect on chytrid infection outcome or prevalence compared to infection with a single isolate. In polyculture, the effect on host growth was most significant in the single chytrid isolate treatment, which was attenuated with the addition of mixed chytrid treatments. Genetic analysis of the resulting population after the experimental period showed a tendency for the chytrid isolate C1 and P. agardhii 1801 to dominate in mixed population samples. Two different interspecific interactions seem to be in play; varied parasite infection strategies allow for the amplification of infection prevalence due to mixed chytrids in a susceptible monoculture, or competition allows for the dominance of a single chytrid isolate in monoculture and the reduction of infection prevalence in a host polyculture. This work thus highlights how interactions between chytrid infections can change the course of epidemic development and harmful algal bloom formation.
蓝藻有各种各样的天敌，如食草动物和病原体，包括真菌病原体在 Chytridiomycota （壶菌）。虽然这些病原体已经在少数几种蓝藻宿主上被描述过，并且被怀疑在生态中发挥了重要作用，但对于种间相互作用以及寄生虫之间的竞争如何影响流行病的发展和水华的形成，我们知之甚少。在这里，从伊利湖的桑达斯基湾（俄亥俄州，美国）分离的三种 Planktothrix agardhii 分离株在单培养和混养中受到了它们专性壶菌真菌病原体 Rhizophydiales sp. 的感染。壶菌分离株作为单分离株或多达三种不同分离株的混合物进行接种。在单培养中，宿主分离株被鉴定为高度易感（P. agardhii 1030）、中度易感（P. agardhii 1808）或主要抵抗（P. agardhii 1801）。在高度易感的宿主分离株上，混合感染壶菌分离株对壶菌的流行有相加作用，导致培养物崩溃，存在 2 或 3 种壶菌分离株。与单独感染一种分离株相比，在中度易感和主要抵抗的分离株上混合感染壶菌分离株对壶菌感染的结果或流行率没有影响。在混养中，在单一壶菌分离株处理中对宿主生长的影响最为显著，而添加混合壶菌处理则减弱了这种影响。实验结束后对种群进行的遗传分析显示，在混合种群样本中，壶菌分离株 C1 和 P. agardhii 1801 有占主导地位的趋势。两种不同的种间相互作用似乎在起作用；不同的寄生虫感染策略允许由于易感单培养物中的混合壶菌而放大感染流行率，或者允许在单培养物中单一壶菌分离株的优势和宿主混合培养物中感染流行率的降低。因此，这项工作强调了壶菌感染之间的相互作用如何改变流行病的发展和有害藻类水华的形成过程。
