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Evolutionary biologists uncover new branch on Tree of Life in rare discovery published in Nature
(Halifax, N.S.) — Scientists at Dalhousie Universityhave discovered a new branch on the ‘Tree of Life’ that no one knew existed. Their findings were published today in the journal Nature and will be critical to better understanding the evolutionary history of life on earth.
“This discovery literally redraws our branch of the ‘Tree of Life’ at one of its deepest points,” explains Alastair Simpson, the lead author of the study and biology professor at Dalhousie. “It opens a new door to understanding the evolution of complex cells—and their ancient origins—back well before animals and plants emerged on Earth.”
The team of biologists used a relatively new scientific technique called single-cell transcriptomics to sequence the first genetic information of two rarely-observed microscopic species belonging to a group of organisms called hemimastigotes. The paper outlines how that genetic information proves that hemimastigotes warrant a rethinking of established “supergroups” on the Tree of Life.
Hemimastigotes are complex cells, like the cells of animals and plants, and belong to the same domain on the Tree of Life: Eukarya. In other words, hemimastigotes share an ancient common ancestor with humans, other animals, fungi and plants. However, since there was no genetic information available on hemimastigotes prior to this study, it was unclear where they belonged within Eukarya.
“It was clear from our analyses that hemimastigotes didn’t belong to any known kingdom-level group, or even to a known ‘super-group’ of several kingdoms together, like the one that includes both animals and fungi,” says Dr. Simpson. “This one little collection of organisms is a whole new group at that level, all on its own. It’s a branch of the Tree of Life that has been separate for a very long time, perhaps more than a billion years, and we had no information on it whatsoever.”
Yana Eglit, a PhD Candidate in Biology at Dalhousie, found the hemimastigotes in a soil sample taken while hiking near Halifax, N.S. In addition to this discovery, Eglit was able to culture one of the two hemimastigotes for the first time, making it easier for scientists to study moving forward.
“It’s an unusual looking group of organisms,” says Eglit, a first author of the study. “The way they behave under the microscope, you won’t immediately spot them... There are likely more representatives in this group that we just simply haven’t met yet.”
These findings are vital for evolutionary biologists striving to piece together how the complex cells of animals, plants, fungi, algae and protozoa have evolved over the last 1-2 billion years. Further, ecologists around the world studying the hugely important roles of microbes on the planet will now be able to identify hemimastigotes in their genetic datasets; this biodiversity would have passed as unidentified until now.
The collaborative research effort was made possible through Dalhousie’s Centre for Comparative Genomic and Evolutionary Bioinformatics (CGEB). The researchers from the Faculties of Science and Medicine have named one of the species Hemimastix kukwesjijk, paying tribute to it being discovered in Nova Scotia—territory of the Mi’kmaq First Nation. “Kukwes” is a “ravenous, hairy ogre” in Mi’kmaq folklore. The team says this predatory microbe looks and behaves similarly.
*The Nature study is titled Hemimastigophora is a novel supra-kingdom-level lineage of eukaryotes. Images of the hemimastigotes are available.
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