Talking multicellularity on Demystifying Science

I had a great time talking about multicellularity, contingency, and all kinds of other things with Dr. Michael Shilo DeLay and Dr. Anastasia Bendebury on the Demystifying Science:

If you prefer to hear than see me blather on, the podcast is available here, but you’ll miss out on my Volvox wall art.

New book on the evolution of multicellularity

I haven’t been blogging much lately, and here’s one of the reasons: Peter Conlin, Will Ratcliff, and I have been editing a book on the evolution of multicellularity, which the publisher says will come out in late March, 2022. It’s available for preorder now, at a 20% discount.

The Evolution of Multicellularity

The Evolution of Multicellularity, cover art by Pedro Márquez-Zacarías

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Jackson Wheat on misunderstanding multicellularity

Jackson Wheat has a new video answering Creation Ministries International’s claims that multicellularity is a problem for evolution. CMI’s strategy seems to be

  1. Bring up a topic in evolutionary biology
  2. Pretend that there haven’t been thousands of scientific papers published on that topic
  3. Make an argument from incredulity as if the question they’re asking hasn’t already been answered

Jackson does a great job tearing down CMI’s assertions one by one.

Choanoflagellates with inversion

Salpingoeca rosetta

Figure 1A from Dayel et al. 2011. Spherical colony of Salpingoeca rosetta. Scale bar = 5 μm.

The closest (known) living relatives of animals are a group of unicellular or colonial filter-feeders known as choanoflagellates. Much of what we know about the evolution of multicellularity in animals comes from comparisons with choanoflagellates. For example, many of the gene families involved in multicellular development in animals, and previously thought to be unique to animals, have turned out to be present in choanoflagellates as well, suggesting that these gene families were present in animal ancestors before they evolved multicellularity. Some multicellular choanoflagellates have even been shown to have differentiated cell types (Laundon et al. 2019):

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Upcoming talks, and some system maintenance

Chlamydomonas colonies from the predation experiment.

Chlamydomonas colonies from the predation experiment.

I’ll be giving a couple of talks on experimental evolution of multicellularity in the next couple of weeks:

  1. University of Georgia Department of Cellular Biology, Tuesday, September 11, 11:00 a.m. in Biological Sciences 404A
  2. Donald Danforth Plant Science Center, Friday, September 20, time and place TBD

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Fungi are weird

I think about the evolution of multicellularity a lot, and I talk about it with colleagues. One of the things we talk about is what general principles we can infer from the many independent origins of multicellularity, for example in land plants, animals, red algae, brown algae, green algae, and fungi. Those are the groups that have evolved what we might call complex multicellularity, and one of the things we notice is that they all develop clonally; that is, they start out as a single cell, and when that cell divides, the daughter cells stick together. We notice that complex multicellularity has never evolved in species with aggregative development, when free-living cells come together to form a multicellular body, as they do in cellular slime molds and myxobacteria. Some aggregative developers have evolved a couple of different cell types, but all of the groups that have reached higher degrees of complexity develop by cell division and the products of cell division staying together. All, that is, except for fungi. Fungi are weird.

Fungi don’t really develop clonally in the way I’ve described, but they don’t really not develop clonally either. That’s because their cells don’t divide in the way we’re used to thinking about, through repeated rounds of mitosis. In mitosis, duplication of the genome is coupled to cell division: the chromosomes duplicate, they move to either end of the cell, then the cell divides. The chromosomes double, then they halve, so the daughter cells end up with the same number as the mother cell. That’s not how it works in fungi. Instead, they form filaments called hyphae (singular hypha) that grow at the tip. In some cases, partitions called septa (singular septum) form behind the growing tip, dividing the hyphae into individual cells. In some cases, no septa form, and each hypha is effectively one long, skinny cell with lots of nuclei (this is called a coenocyte).

So fungi don’t really develop by repeated rounds of cell division in the same sense that animals, plants, etc. do. Hyphae just grow, and they are divided into cells as sort of an afterthought, if they are divided into cells at all. Fungi with coenocytic (or aseptate) hyphae aren’t really even multicellular in the same sense as plants and animals are. Different people have different qualifications for what counts as multicellular, but it’s a stretch to call something multicellular that doesn’t have multiple cells. Fungi are weird.

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Debunked by the Institute for Creation Research

Folks, it’s been fun. I feel like I had a pretty good run as a scientist. I met some amazing people, went to beautiful places, and learned things I never would have imagined (Hodgkinia, WTF?!). With all my frustrations and failures, I’ve never once regretted going back to school and becoming a biologist. But now I need to close the door on all of that and find a new way to make a living.

See, the main project I’ve been working on for the last six years, the one that was supported by a NASA postdoctoral fellowship, and that just came out in Scientific Reports, has been debunked:

ICR screenshot [Read more…]