“Aerobic respiration was thought to be ubiquitous in animals, but now we confirmed that this is not the case,” Huchon explains. “Our discovery shows that evolution can go in strange directions. Aerobic respiration is a major source of energy, and yet we found an animal that gave up this critical pathway.” – lead researcher Prof. Dorothee Huchon of TAU.

Life science researchers at Tel Aviv University (TAU) have stumbled upon a non-breathing animal, challenging current understanding of the animal world, according to a study published in the Proceedings of the National Academy of Sciences of the United States of America.

The research, led by Prof. Dorothee Huchon of the School of Zoology at TAU’s Faculty of Life Sciences and Steinhardt Museum of Natural History, detailed the 10-celled parasite organism called Henneguya salminicola that is found in the muscles of salmon. The research was supported by the US-Israel Binational Science Foundation, and conducted along with Prof. Paulyn Cartwright of the University of Kansas, and Prof. Jerri Bartholomew and Dr. Stephen Atkinson of Oregon State University.

“The parasite’s anaerobic nature was an accidental discovery,” TAU said in a statement. “While assembling the Henneguya genome, Huchon found that it did not include a mitochondrial genome. The mitochondria are the powerhouse of the cell where oxygen is captured to make energy, so its absence indicated that the animal was not breathing oxygen.”

The animal itself, a “myxozoan relative” of jellyfish and corals, apparently gave up on breathing and consuming oxygen in order to produce energy, somewhere along its evolutionary track.

“Aerobic respiration was thought to be ubiquitous in animals, but now we confirmed that this is not the case,” Huchon explains. “Our discovery shows that evolution can go in strange directions. Aerobic respiration is a major source of energy, and yet we found an animal that gave up this critical pathway.”

Fungi, amoebas or ciliate lineages living in oxygen-poor environments abandoned the need to consume fresh air quite some time ago, after their evolutionary trajectories followed an anaerobic path. The findings allude to the possibility that the same type of occurrence could happen to an animal if the conditions are right.

“Its genome was sequenced, along with those of other myxozoan fish parasites,” TAU said in a statement.

Before the discovery, experts were unsure whether organisms within the animal kingdom could survive without oxygen, given that animals are “multicellular, highly developed organisms, which first appeared on Earth when oxygen levels rose.” The findings are important for future evolutionary research.

“It’s not yet clear to us how the parasite generates energy,” Huchon said. “It may be drawing it from the surrounding fish cells, or it may have a different type of respiration such as oxygen-free breathing, which typically characterizes anaerobic non-animal organisms. It is generally thought that during evolution, organisms become more and more complex, and that simple single-celled or few-celled organisms are the ancestors of complex organisms.

“But here, right before us, is an animal whose evolutionary process is the opposite. Living in an oxygen-free environment, it has shed unnecessary genes responsible for aerobic respiration and become an even simpler organism.”

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To read about this discovery from TAU Newsroom:

TAU researchers find non-oxygen breathing animal

TAU Researchers Discover Unique Non-Oxygen Breathing Animal