Cells, colonies, and clones: individuality in the volvocine algae

Biological Individuality

As I mentioned previously, I have a chapter in the newly published book Biological Individuality, Integrating Scientific, Philosophical, and Historical Perspectives. The chapter was actually written nearly five years ago, but things move more slowly in the philosophy world than that of biology. Finally, though, both the print and electronic versions are now available; here is the electronic version of my chapter. The book currently has no reviews on Amazon, so if you want to give it a read, yours could be the first. If you’re interested in current and historical views on individuality, there is a lot of good stuff in here, including contributions by Scott Lidgard & Lynn Nyhart, Beckett Sterner, Andrew Reynolds, Snait Gissis, Olivier Rieppel, Michael Osborne, Hannah Landecker, Ingo Brigandt, James Elwick, Scott Gilbert, and Alan Love & Ingo Brigandt.

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New review of green algal sex

Hiroyuki Sekimoto from Japan Women’s University has published a review of sexual reproduction in the volvocine algae and in the Charophyte Closterium in the Journal of Plant Research. In addition to a brief description of the Chlamydomonas sexual cycle, it includes a succinct review of the genetics of sex and sex determination. Unfortunately, the article is paywalled, and my inquiry to the author has so far gone unanswered.

Figure 1 from Sekimoto 2017. The life cycle of Chlamydomonas reinhardtii. Vegetative cells (V) di erentiate into mt+ and mt− gametes (G) during nitrogen starvation (−N). Mating types are restricted by mating-type loci (+ and −). When gametes are mixed, the plus and minus agglutinin mol- ecules on their agellar surfaces adhere to each other, and this adhe- sion results in increased intracellular cAMP levels. The signal trig- gers gamete cell wall release and mating-structure activation. Cells then fuse to form binucleate quadri agellated cells. Zygotes with thick cell walls germinate in response to light and nitrogen supple- mentation, and undergo meiosis to release four haploid vegetative cells

Figure 1 from Sekimoto 2017. The life cycle of Chlamydomonas reinhardtii. Vegetative cells (V) differentiate into mt+ and mt− gametes (G) during nitrogen starvation (−N). Mating types are restricted by mating-type loci (+ and −). When gametes are mixed, the plus and minus agglutinin molecules on their flagellar surfaces adhere to each other, and this adhesion results in increased intracellular cAMP levels. The signal triggers gamete cell wall release and mating-structure activation. Cells then fuse to form binucleate quadriflagellated cells. Zygotes with thick cell walls germinate in response to light and nitrogen supplementation, and undergo meiosis to release four haploid vegetative cells.

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Rediscovered after two thirds of a century: Pleodorina sphaerica

Pleodorina sphaerica

Figure 1 from Nozaki et al. 2017. Pleodorina sphaerica.

There really aren’t enough people looking for volvocine algae. There’s a suspicious tendency for the geographical centers of volvocine diversity — southern Africa, central North America, southeast Asia — to include the home institutions of phycologists studying volvocine diversity — Mary Pocock, Richard Starr, Hisayoshi Nozaki, respectively. I find it much more likely that this is an artifact of sampling effort than that, for example, central Africa and Central and South America are depauperate of volvocine algae.

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Look what came in the mail yesterday!

Biological Individuality

A project started five years ago has finally borne fruit. In May, 2012 I joined a group of philosophers, historians, and biologists in Philadelphia for the Cain ConferenceE pluribus unum: Bringing biological parts and wholes into historical and philosophical perspective.” The meeting was organized by Lynn Nyhart and Scott Lidgard, with the goal

…to pursue the question: How can historians, philosophers, and biologists help each other to understand part-whole relationships in biology, both today and in the past?

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Invasive Pleodorina indica in Poland

Figure 3 B-I from Knysak and Żelazna-Wieczorek 2017. Pleodorina indica (Iyengar) H. Nozaki 400x.

Figure 3 B-I from Knysak and Żelazna-Wieczorek 2017. Pleodorina indica (Iyengar) H. Nozaki 400x.

A new paper in Oceanological and Hydrobiological Studies reports a massive bloom of Pleodorina indica in a reservoir in central Poland. Piotr Knysak and Joanna Żelazna-Wieczorek sampled the reservoir on the Olechówka River in Łódź during the summer of 2015 and found that P. indica made up ~95% of the algae collected.

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Sex change (in Volvox)

Alexey Desnitskiy from Saint Petersburg State University has published a new review of sexual development in the genus Volvox in the International Journal of Plant Reproductive Biology. 

The article includes an up-to-date review of Professor Desnitskiy’s own work describing four developmental “programs” in the various species of Volvox:

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What is a (Volvox) species?

Hisayoshi Nozaki and colleagues have just described some Volvox samples from two lakes and a pond in Japan.

Figure 1A from Nozaki et al. 2016. Volvox sp. Sagami asexual spheroid with daughter colonies (d).

Figure 1A from Nozaki et al. 2016. Volvox sp. Sagami asexual spheroid with daughter colonies (d).

The newly collected strains have a lot in common with another recently described species, Volvox ferrisii, but there are some important differences as well:

…it could be clearly distinguished from all previously described monoecious species of Volvox sect. Volvox by its small number of eggs or zygotes (5–25) in sexual spheroids, with short acute spines (up to 3 μm long) on the zygote walls and elongated anterior somatic cells in asexual spheroids.

In spite of these differences, Nozaki and colleagues stop short of calling the newly collected strains a new species. Why?

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It’s not evolution, just adaptation

…”evolve” is not the correct term. The microbes adapted. – Cornelius Hunter

We heard several accusations during the recent Presidential campaign that one or the other candidate, or an interviewer, had taken a quote out of context. Of course, every quote is taken out of context. That’s what a quote is; otherwise it’s just the whole speech, or interview, or whatever. The important question is whether or not it’s taken out of context in a way that changes its meaning.

One thing I don’t do, and never have done, on this blog is intentionally misrepresent other people’s positions.  The quote above, from a recent post by Cornelius Hunter on Evolution News and Views, means just what it says. He really is arguing that microbial adaptation observed in Lenski-style experiments is not evolution.

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Initiation of cell division in Chlamydomonas

Deborah Shelton and colleagues have published a new article arguing that the reigning model of cell division initiation in Chlamydomonas reinhardtii needs to be revised [full disclosure: Dr. Shelton and I were labmates in Rick Michod’s lab at the University of Arizona]. The evolution of multicellularity almost certainly involved changes in cell cycle regulation; for example, there is good evidence that changes to the cell cycle regulator retinoblastoma were involved in the initial transition to multicellular life in the volvocine algae. So understanding cell cycle regulation is vital for understanding the evolution of multicellularity.

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