| Summary: | Cyanobacterial blooms are an omnipresent and well-known result of eutrophication and climate change in aquatic systems. Cyanobacteria produce a plethora of toxic secondary metabolites that affect humans, animals and ecosystems. Many cyanotoxins primarily affect the grazers of phytoplankton, e.g., <i>Daphnia</i>. The neurotoxin anatoxin-α has been reported world-wide; despite its potency, anatoxin-α and its effects on <i>Daphnia</i> have not been thoroughly investigated. Here, we investigated the effects of the anatoxin-α-producing <i>Tychonema</i> on life-history parameters and gene expression of nicotine-acetylcholine receptors (NAR), the direct targets of anatoxin-α, using several <i>D. magna</i> clones. We used juvenile somatic growth rates as a measure of fitness and analyzed gene expression by qPCR. Exposure to 100% <i>Tychonema</i> reduced the clones’ growth rates and caused an up-regulation of NAR gene expression. When 50% of the food consisted of <i>Tychonema</i>, none of the clones were reduced in growth and only one of them showed an increase in NAR gene expression. We demonstrate that this increased NAR gene expression can be maternally transferred and that offspring from experienced mothers show a higher growth rate when treated with 50% <i>Tychonema</i> compared with control offspring. However, the addition of further (anthropogenic) stressors might impair <i>Daphnia</i>’s adaptive responses to anatoxin-α. Especially the presence of certain pollutants (i.e., neonicotinoids), which also target NARs, might reduce <i>Daphnia</i>’s capability to cope with anatoxin-α.
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