Scientists Baffled to Find First Animal on Earth That Does Not Breathe, Unsure How It Generates Energy

In 2020, researchers shared with the world about their discovery of a multicellular creature that does not breathe. The being in question is Henneguya salminicola, a parasitic blob, stated Live Science. This was a breakthrough finding because, before the analysis of H.salminicola, no creature was observed to be without respiratory cells. Researchers believe the unique phenomenon occurred in this particular parasite because of its lifestyle. Findings regarding H.salminicola's unique state were published in the journal Proceedings of the National Academy of Sciences. 

H.salminicola uses fish and underwater worms as its host. The creature infects the muscles of these aquatic organisms to gather nutrients required for survival. In these life processes H.salminicola poses no need of turning oxygen into energy. This implies that the respiratory mechanism that could have been present in this parasite in the past was not working much. Researchers believe that with time the respiratory genes phased out of H.salminicola due to a lack of function.

Researchers made the discovery accidentally while sequencing the "Henneguya" genome, according to CBS News. The sequencing unveiled that H.salminicola had no mitochondrial genes—the cell powerhouse that contains the respiratory mechanism. The mechanism's main function is to generate energy for the creature. The discovery made researchers question how H.salminicola generated its required energy without the necessary apparatus. "It's not yet clear to us how the parasite generates energy," Tel Aviv University professor and lead author, Dorothee 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."

Though the lack of respiratory genes was a new finding, this was not the first time researchers had seen unexpected developments in this kind of parasite, according to Live Science. Myxozoa class, the group to which H.salminicola belongs, has jellyfish as its direct ancestors. But throughout evolution, they have not carried any jellyfish traits. "They have lost their tissue, their nerve cells, their muscles, everything," Huchon explained. "And now we find they have lost their ability to breathe."

Experts noted that the loss of genes has been beneficial for this group of parasites. Researchers believe that the unique phenomenon enables them to reproduce quickly and be highly effective in taking over their host. This kind of 'evolution' for better survival intrigued the researchers. "Animals are always thought to be multicellular organisms with lots of genes that evolve to be more and more complex," Huchon explained. "Here, we see an organism that goes completely the opposite way. They have evolved to be almost unicellular."

The discovery has changed the way experts perceived the evolution of animal kingdoms and the processes they considered to be advanced like aerobic respiration, according to CBS News. "Aerobic respiration was thought to be ubiquitous in animals, but now we confirmed that this is not the case," Huchon said. "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."