Convergent evolution of soma in Astrephomene

A new paper by Shota Yamashita and colleagues explores the genetic basis for soma in one of the most mysterious volvocine algae, Astrephomene gubernaculifera. By combining whole genome sequencing with cell-type specific transcriptomics, they have shown that the gene or genes controlling germ/soma differentiation in Astrephomene are different from those in Volvox carteri, but the resulting cell-type specific differences in gene expression are similar between the two.

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Meet Eudorina compacta!

Nozaki et al. 2020 Fig. 2A & B

Fig 2A & B from Nozaki et al. 2020. Light microscopy of Eudorina compacta Nozaki sp. nov. originating from Lake Victoria. (A) Surface view of 32-celled vegetative colony showing compactly arranged cells. (B) Optical section of 32-celled vegetative colony showing a hollow structure.

Hisayoshi Nozaki and colleagues have described another new species of volvocine algae, a member of the genus Eudorina from Lake Victoria in Tanzania. Unlike most species in this genus, the cells of Eudorina compacta are tightly packed around the surface of the colony, which is ellipsoidal. They coexist in Lake Victoria with Colemanosphaera charkowiensis, another species that Dr. Nozaki and colleagues described in 2014.

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A series of fortunate events

Salomé and Merchant 2019 Fig. 1

Figure 1 from Salomé and Merchant 2019. Taxonomic Basis of Chlamydomonas and Volvox. Ehrenberg’s drawings of Chlamydomonas and Volvox cells, published in 1838. Cells that belong to the same species are indicated by Roman numerals in the right panel. I, Gonium pectorale; II, Gonium punctatum; III, Gonium tranquillum; IV, Gonium hyalinum; V, Gonium glaucum; VI, Eudorina elegans; VII, Syncrypta volvox; VIII, Sphaerosira volvox; IX, Synura uvella; X, Chlamidomonas pulvisculus; XI, Uroglena volvox. The species was identified as Chlamidomonas pulvisculus but renamed Chlamydomonas reinhardtii in 1888.

In a new(-ish) article in The Plant Cell, Patrice Salomé and Sabeeha Merchant review the history and utility of the green alga Chlamydomonas reinhardtii as a model organism. The article discusses the advantages of Chlamy as a model organism, the scientific questions it has been used to explore, the history of Chlamy research, the characteristics of the species, the existing resources and databases, and genetic and genomic techniques. It’s a good introduction to Chlamy research in a more easily-digestible form than the massive, three-volume Chlamydomonas Sourcebook.

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Volvox rousseletii in Japan

A few years back, I invited Dr. Hisayoshi Nozaki to visit the University of Montana, and to my surprise, he came. In fact, five Japanese researchers came to Missoula for the better part of a week: Dr. Nozaki, Dr. Noriko Ueki, Dr. Osami Misumi, and two undergraduate researchers. We found a species, Volvox capensis, which had previously only ever been found in South Africa, in Ninepipe Reservoir (about an hour north of Missoula).

Now Ryosuke Kimbara and colleagues have reported another apparent long-distance traveller. In a new paper in PLoS One, they report finding Volvox rousseletii, previously reported only in Africa, in Lake Sagami in Japan. Volvox rousseletii is a member of the group of species known as Volvox section Volvox (also sometimes referred to as Euvolvox), which includes the largest species (in terms of cell number) and evolved independently of the other species in the genus Volvox.

Kimbara Fig. 1

Figure 1 from Kimbara et al. 2019. Light microscopic features of asexual spheroids in culture of Volvox rousseletii strain v-sgm-17 from Lake Sagami, Japan. (A) Mature spheroid showing daughter spheroids (d). (B-D) Part of spheroids. (B) Top view of individual sheaths (asterisks) of somatic cells stained with methylene blue. (C) Top view of somatic cells with thick cytoplasmic bridges (b). (D) Side view of elongate-ellipsoidal, anterior somatic cell with stigma (s) and pyrenoid (p) in the chloroplast. (E) Developing embryo just after inversion, showing gonidia (g) of the next generation.

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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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Embryogenesis in Gonium and Tetrabaena

Back when I was a cocky grad student, I wrote a paper that was, in some ways, critical of the work of one of the biggest names in my field. David Kirk, who passed away last year, was among the most important figures in establishing Volvox as a model system for development, genetics, and evolution, among other things. He had published a paper that I thought was unnecessarily progressivist, and I said so in terms that, in retrospect, could have been more diplomatic. In response, Dr. Kirk, whom I had never met, sent me a very thoughtful email thanking me for pointing out some of the problems and politely disagreeing on some other points. Its tone was kind and respectful when annoyed and argumentative would have probably been justified.

In that email, he offered a bet, the stakes of which were to be a beer, that one of the things I had suggested would turn out to be wrong. The issue had to do with inversion, a process that the (mostly) spheroidal algae in the family Volvocaceae undergo during development. I have written about inversion many times on Fierce Roller; in a nutshell, these algae start their lives inside-out, with their flagella on the inside, and invert to get the flagella on the outside, where they can be used for swimming. Their relatives in the genus Gonium also undergo a process of partial inversion, changing from cup-shaped (with the flagella on the concave side) to flat or slightly cup-shaped in the other direction. Dr. Kirk had interpreted Gonium‘s partial inversion as a probable intermediate step that led to the complete inversion characteristic of the Volvocaceae. My reconstructions suggested that incomplete inversion in Gonium had evolved separately from complete inversion in the Volvocaceae, and Dr. Kirk bet me that this would turn out to be wrong.

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Why carteri?

It’s embarrassing, really. I’ve been studying Volvox and its relatives for 15 years now, and until today I couldn’t have told you who the most famous member of the group, Volvox carteri, was named for. Sure, I know Colemanosphaera is named for Annette Coleman, Volvox ferrisii for Patrick Ferris, and Volvox kirkiorum (“of the Kirks”) for David and Marilyn Kirk, but that’s because they were all named after I started studying Volvox.

But do you recall…the most famous algae of all?

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