Our new book has gone to the printer. The ebook is already available, and the hardcover is available for preorder. The publisher has provided a discount code good for 20% off through June 30, 2022, ASM04.
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.
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, cover art by Pedro Márquez-Zacarías
Journey to the Microcosmos produces outstanding videos of microscopic life, and they have featured the volvocine algae before. This new video is entirely focused on the volvocines and on the evolution of multicellularity, and it’s really good.
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
Jackson does a great job tearing down CMI’s assertions one by one.
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):
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:
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.
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:
Just after my conversation with Jackson Wheat, R. J. Downard invited me to his weekly live stream, Evolution Hour. We talked about the evolution of multicellularity, heritability, and, of course, intelligent design.
