The cyanobacteria blooms that plague western Lake Erie each summer are both an unsightly nuisance and a potential public health hazard, producing liver toxins that can be harmful to humans and their pets.
But the toxins produced in cyanobacteria blooms may also have protective effects on sand-grain-sized lake animals that ingest them, much as the toxins in milkweed plants protect monarch butterflies from parasites, according to a new study from University of Michigan ecologists.
The laboratory-based study shows that tiny, shrimp-like freshwater crustaceans called Daphnia can gain protection from fungal parasites by consuming toxins produced by bloom-forming cyanobacteria. Commonly known as water fleas, Daphnia play a key role in freshwater food webs and are a vital food source for many fish.
The U-M researchers plan follow-up studies to see if the protective effects they observed in the lab are also occurring in lakes. They’ll also explore the potential of developing anti-fungal drugs for human use.
The study is published online in the journal Proceedings of the Royal Society B. The first author is Kristel Sánchez, who did the work for her master’s thesis in the U-M Department of Ecology and Evolutionary Biology. Co-authors include her faculty advisers, U-M ecologists Mark Hunter and Meghan Duffy.
“This paper shows that Daphnia living in Michigan lakes can gain protection from fungal parasites through the toxins that are present in bloom-forming cyanobacteria,” said Hunter, who has studied monarchs at U-M’s Biological Station for more than a decade.
“This is an amazing aquatic parallel of the monarch butterflies, which gain protection from their parasites from the toxins in milkweed. It suggests that animal medication may be even more common than we thought, extending into the aquatic realm.”
The Proceedings of the Royal Society B paper is titled “Toxins or Medicines? Phytoplankton diets mediate host and parasite fitness in a freshwater system.” The other author, in addition to Sánchez, Duffy and Hunter, is former U-M undergraduate Naomi Huntley, who worked in Duffy’s lab.
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*Full image (above) caption: Microscope image of two Daphnia dentifera that fed on different diets and were exposed to a fungal pathogen. The top Daphnia fed on a nutritious green algae. She is larger and has several embryos in her brood chamber but is infected with a virulent fungal pathogen. The animal on the bottom fed on a toxic cyanobacterium. As a result, she is smaller and only has one developing embryo but is not infected with the pathogen (and, therefore, will live longer).