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Our Common Ancestor with the Fungi

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#1 WalkingCatfish



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Posted 23 November 2018 - 12:55 PM

I was watching Paul Stamets on Joe Rogan's channel, the other day, and I see he's still claiming that animals like us are descended directly from fungi. I love and admire Stamets, and he has an amazing hat, but he's stretching the truth, there. :wink: While it's true that fungi and animals are closely related, our common ancestor was not something you could call a fungus.

So, if we were to travel back in time to the fork in the tree--a billion years ago, give or take--what would our shared ancestor be like? A couple of years back, a group in Spain listed some of the features it would have had:

We share a large branch on the tree of life with our fungal friends. This is the superkingdom Opisthokonta, proposed by Tom Cavalier-Smith back in the 80s, and since confirmed by many genetic analyses. There are other critters on that branch. Most are single-celled organisms, though a few, like our little cousins, the choanoflagellates, form simple colonies. All of the opisthokonts are thought to share an odd ancestral trait: certain of their cells possess a single rear-mounted flagellum, similar to the "tail" that drives animal sperm cells. Some fungi (the chytrids) have a similar whiplike tail. It has been lost in most other "opisthokonts," but was certainly present in our common ancestor.

Here are some zoospores of chytrid fungi...think of them as fungus-sperm :D


chytrid zoospores.jpg

This solitary ass-mounted whiplash flagellum is a bit unusual, actually. Most flagellated cells have more than one whip, and these are typically mounted at the front end of the cell. When used for locomotion, they kind drag the cell along, rather than propelling it from behind. Front whip drive, if you will.

So, the ancestor we share with fungi probably had a flagellum. It also would have been a kind of amoeba. That is, it would have had the cellular superpower of being able to extend long pseudopods, protrusions of the cell body used for feeding and/or locomotion. These would have been thin and stringy pseudopods of a kind called "filose" (filopodia). Here's a short video I recorded of Nuclearia, a critter more closely related to the fungi than we are, showing some of these filopodia in action:

Finally, according to Torruella et al., our shared ancestor would have been able to synthesize chitin, the polysaccharide that makes up the cell walls of fungi and also the exeskeletons of insects, crustaceans, etc.  

So, there you have it. The ancestor you share with your shrooms was a filose amoeba, like the Nuclearia I filmed, but with a single rump-rope. It ate bacteria for a living, nomming them by phagocytosis. It also had a biochemical toolkit for making chitin.

In other words, another weird thing that in a weird world. :biggrin: Something to think about, next time you're chewing on our little mushroom brothers.

Edited by WalkingCatfish, 23 November 2018 - 01:00 PM.

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