Children are taught that all living organisms — from animals, plants, and fungi to bacteria and single-celled organisms — belong to specifically different categories of organic life. A new discovery by Tel Aviv University researchers and international collaborators is poised to redefine the very criteria used to define and classify these animals.
Researchers have found that a close cousin of the jellyfish has evolved over time into a microscopic parasite. The finding represents the first case of extreme evolutionary degeneration of an animal body.
The research was led by Prof. Dorothée Huchon of TAU's Department of Zoology and Prof. Paulyn Cartwright of the University of Kansas, in collaboration with Prof. Arik Diamant of Israel's National Center for Mariculture and Prof. Hervé Philippe of the Centre for Biodiversity Theory and Modelling, CNRS, France. It was published this week in the Proceedings of the National Academy of Sciences.
What makes a myxozoan
The international research used genome sequencing to find that myxozoans, a diverse group of microscopic parasites that infect invertebrate and vertebrate hosts, are actually are highly degenerated cnidarians — the category or phylum that includes jellyfish, corals and sea anemones.
"These micro-jellyfish expand our basic understanding of what makes up an animal," said Prof. Huchon. "What's more, the confirmation that myxozoans are cnidarians demands the re-classification of myxozoa into the phylum cnidaria."
Despite the radical changes in its body structure and genome over millions of years, the myxozoa have retained some of the basic characteristics of the jellyfish, including the essential genes to produce the jellyfish stinger.
"The myxozoa are microscopic — only a few cells measuring 10 to 20 microns across — and therefore biologists assumed that they were single-celled organisms," said Prof. Huchon. "But when we sequenced their DNA, we discovered the genome of an extremely strange macroscopic marine animal."
The discovery of the dramatic change from macroscopic marine animal to microscopic parasite is interesting on its own, but it may also have commercial applications, as myxozoa commonly plague commercial fish stock such as trout and salmon.
"Some myxozoa cause a neurological problem in salmon called 'whirling disease,'" said Prof. Huchon. "These fish parasites cause tremendous damage to the fish industry, and unfortunately there is no general treatment against them. We hope that our data will lead to a better understanding of the biology of these organisms and the development of more effective drugs to fight against myxozoa."
The researchers are currently studying the evolution in myxozoa of genes that form the stinging organ of jellyfish. The study was funded by the National Science Foundation, the Binational Science Foundation, and the Israel Science Foundation.
American Friends of Tel Aviv University supports Israel's most influential, comprehensive, and sought-after center of higher learning, Tel Aviv University (english.tau.ac.il). TAU ranked #75 globally and #1 in Israel in a 2015 Reuters survey of the 100 most innovative universities. It is one of a handful of elite universities rated as the best producers of successful startups, and TAU alumni rank #9 in the world for the amount of venture capital they attract.