Have you ever seen a hemimastigote? It’s just a kind of bacteria, right? Not so. There may or may not be aliens, but there are strange creatures to explore right under our noses and plenty of discoveries still to be made in evolutionary biology. Recently in Canada, genetic analysis of an odd microbe known as a hemimastigote revealed it to belong to an entirely new fundamental branch on the tree of life under eukaryotes. We humans are eukaryotes. So are yeasts and corn. Eukaryotes include plants, animals, fungi as well as a catch-all group known as Protists. Ah, so a hemimastigote is a Protist, right? That’s the thing… it isn’t, at least it does not fit any major kind of Protist we’ve classified yet.
Here are a few more hemimastigote microscope images:
Now you have seen the hairy hungry microscopic ogres living in Canadian dirt. Strange beasts. How do we classify them?
Where do hemimastigotes fit in? Here is what the genetics show:
This may not mean much at first glance because it is a zoomed in limited picture of the tree, but the genetics of hemimastigotes show they do not fit into any existing kingdom of eukaryotes. They are not plants, fungi or animals and they do not fit into any existing protist groups. (The Kingdom of Protists isn’t a real group that has a common ancestor other than being eukaryotes, but they are lumped together as such for simplicity.)
What the above graph shows is that the hemimastigotes are different enough from every other protist yet discovered so as to warrant their own unique branch on the tree. For convenience, most will still consider them to be in the Protist group, I suspect.
Do you see us in the above graph? We humans are in there. Each group tells us something about all creatures within it, so we can learn a lot about what it is to be human by studying each of the groups to which we belong. You will recognize some:
We are in the Unikonts or Amorphea taxonomic supergroup. We are under the Obazoa, as Opisthokonts and under that group we are in Holozoa. Under that Filozoa, Choanozoa, and finally Animalia. Ah, Animalia, that one you’ve heard of, most likely.
Within the animal kingdom, we are in the phylum of Chordates. Under the chordates we are Vertebrates, in the Mammal class, order of Primates, Haplorhini sub order, simians (Simiiform) within that group, Catarrhini subdivision, and within that we are Apes (Hominoidea) from a branch of Old World tailless anthropoid primates native to Africa and Southeast Asia. Under the apes we are in the great apes group:
The Hominidae, whose members are known as great apes or hominids, are a taxonomic family of primates that includes eight extant species in four genera: Pongo, the Bornean, Sumatran and Tapanuli orangutan; Gorilla, the eastern and western gorilla; Pan, the common chimpanzee and the bonobo; and Homo, which includes modern humans and its extinct relatives (e.g., the Neanderthal), and ancestors, such as Homo erectus.
This brings us back to the graph above where you might have seen us if you looked carefully. We are under Homo, our genus.
Virtually all eukaryotes belong to either the animal, plant, or fungi kingdoms, but some eukaryotes cannot be classified as such, and are deemed protists. Not satisfied with these broad designations, scientists created six “super-groups” for the eukaryote domain: Sar/Telonemia, Haptophyta/Centrohelida, Archaeplastida/Picozoa (this group contains plants), Cryptista (this group contains algae), Discoba, and Amorphea (this group contains animals and fungi).
When you have powerful tools such as genetic analysis of millions of different samples of life from everywhere on earth, a complicated picture starts to emerge. That picture is the tree of life which shows how life evolved and is related.
Early approaches to describe the tree of life distinguished organisms based on their physical characteristics and metabolic features. Molecular methods dramatically broadened the diversity that could be included in the tree because they circumvented the need for direct observation and experimentation by relying on sequenced genes as markers for lineages. Gene surveys, typically using the small subunit ribosomal RNA (SSU rRNA) gene, provided a remarkable and novel view of the biological world…
The full tree of life is huge and is still being updated. As life is still evolving, it will never be finished.
Click for larger view.
Join me in welcoming hairy hungry hemimastigotes to the tree of life. We don’t have any particular use for them at this point, but they could say the same of us.