Scientists from the University of Kansas have published research in the journal Proceedings of the National Academy of Sciences suggesting that jellyfish actually evolved into tiny organisms living inside vertebrate hosts or infecting invertebrates as parasites – a research that could inform the redefinition of what constitutes an animal - according to researchers from Kansas University.
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Genome sequencing of myxozoans show that jellyfish evolved into microscopic parasites that are cnidarians, and Paulyn Cartwright, associate professor of ecology and evolution biology at Kansas University and leader of the project team noted that scientists are now tasked with investigating how cnidarians became the way they are.
Although myxozoan genome appeared very simplified, the KU Medical Center’s Genome Sequencing Facility was able to prove that parasitic micro jellyfish evolved by shedding a few cells to become sea pests with stinging tentacles.
“These were 20 to 40 times smaller than average jellyfish genomes,” Cartwright said. “It’s one of the smallest animal genomes ever reported. It only has about 20 million base pairs, whereas the average Cnidarian has over 300 million. These are tiny little genomes by comparison.”
Researchers were able to establish that the stinger or nematocyst of the myxozoa retains genome and structure of the jellyfish despite its evolution over several million years. “Because they’re so weird, it's difficult to imagine they were jellyfish,” Cartwright said. “They don’t have a mouth or a gut. They have just a few cells. But then they have this complex structure that looks just like stinging cell of cnidarian. Jellyfish tentacles are loaded with them — little firing weapons.”
The results of this research have wide applicability, and among these is the fact that myxozoa plagues trout and salmon among other fish stock, affecting their commercial value. Cartwright disclosed that these parasites are wide and some of them infect fish and even destroy aquacultures, while causing a neurological problem that makes salmon swim in circles.
To this extent, the discovery that myxozoans are cnidarians might inform the redefinition or re-classification of myxozoa into the phylum cnidaria – further providing what knowledge is needed to fully understand what constitutes an animal.
Scientists say the biology of these parasites are never evolutionary in origin, and even though they are microscopic, they have some cells measuring between 10-20 microns. Scientists earlier thought they were single-celled organisms, but a mapping of their DNA shows they are just weird animals.
“Hox genes are one example, which are important to development of all animals, and these lack them,” she said. “But Myxozoa is definitely an animal because its evolutionary origin is shared with jellyfish, and we use species’ ancestry to define them. But animals are usually defined as macroscopic multicellular organisms, and this is not that. Myxozoa absolutely redefines what we think of as animal.”
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Sponsored by the National Science Foundation, Binational Science Foundation, and Israel Science Foundation, Cartwright and other colleagues such as E. Sally Chang, KU doctoral student; Dorothée Huchon and Moran Neuhof, Tel-Aviv University; Nimrod Rubinstein, Harvard University; Arik Diamant, of Israel’s National Center for Mariculture, and Hervé Philippe of the Centre for Biodiversity Theory and Modelling Station d’Ecologie Expérimentale du CNRS among others carried out the research.