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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J. S. Huxley part 2: Volvox

Last time, I wrote about Julian Huxley’s 1912 book, The Individual in the Animal Kingdom, and his use of the volvocine algae as an example. I liked most of what he had to say, though I took issue with his assertion that

…all the other members of the family except Volvox…are colonies and nothing more—their members have united together because of certain benefits resulting from mere aggregation, but are not in any way interdependent, so that the wholes are scarcely more than the sum of their parts.

This is, of course, a matter of how we define a multicellular organism, but I think any definition that excludes, for example, Eudorina, is not a very useful one.

This time, I’ll look at the rest of what Huxley had to say about the volvocine algae, most of which is about Volvox:

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J. S. Huxley part 1: Gonium

Julian Huxley was one of the biologists responsible for the merging of Mendelian genetics and Darwinian evolution in the early 20th century, the modern synthesis. His most influential work was Evolution: The Modern Synthesis, published in 1942. Thirty years earlier, though, he published a book on biological individuality, The Individual in the Animal Kingdom. Thankfully, the copyright on this book has expired, so it is now part of the public domain, and a scanned version is available for free in pdf and epub versions from Google.

Huxley Cover

Any book with Volvox on the cover can’t be all bad!

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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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Pleodorina inversion

Stephanie Höhn and Armin Hallmann have published a detailed study of the developmental process of inversion in Pleodorina californicaPleodorina is one of the two genera we usually refer to as ‘partially differentiated’ (the other is Astrephomene), meaning that some of their cells are specialized for motility and never reproduce (soma) and some perform both motility and reproductive functions. P. californica is pretty big, up to about 1/3 of a millimeter, easily visible to the naked eye (though you’d need better vision than mine to make out any details).

Stephanie Höhn sampling a pond near Cambridge University during the Volvox 2015 meeting.

Stephanie Höhn sampling a pond near Cambridge University during the Volvox 2015 meeting.

Like all members of the family Volvocaceae, P. californica undergoes complete inversion during development:

After the completion of the cell division phase and before inversion, the embryos of Gonium, Pandorina, Eudorina and Pleodorina consist of a bowl-shaped cell sheet, whereas the embryonic cells of Volvox form a spherical cell sheet. With exception of the genus Astrephomene, all multicellular volvocine embryos face the same “problem”: the flagellar ends of all the cells point toward the interior of the bowl-shaped or spherical cell sheet rather than to the exterior, where they need to be later to function during locomotion. [References removed]

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Multicellularity rundown

Too many papers, not enough time: each of these deserves a deep dive, but my list just keeps getting longer, so I’m going to have to settle for a quick survey instead. To give you an idea of what I’m up against, these papers were all published (or posted to bioRxiv) in July and August, 2016. By the time I could possibly write full-length posts about them all, there would probably be ten more!

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Graduate student position in the Nedelcu lab

If you’re a fan of Volvox and the volvocine algae and have recently received an undergraduate degree in biology or a related field, now’s your chance to get serious about studying them. Aurora Nedelcu is looking for a graduate student to join her lab at the University of New Brunswick. Professor Nedelcu is a major player in the Volvox community, having published foundational papers on diverse aspects of volvocine biology and organized the first two international Volvox meetings. This is a great opportunity to join a vibrant and growing research community:

A graduate student position is available in the laboratory of Aurora Nedelcu, in the Department of Biology at the University of New Brunswick, Fredericton, CANADA. Research in our laboratory is directed towards understanding general, fundamental issues in evolution – such as the evolution of multicellularity, development, cell differentiation, sex, programmed cell death, altruism.  Our research is rooted in the framework of transitions in individuality and evolution of complexity (at a conceptual level), and of cellular responses to stress (at a more mechanistic level).  The experimental model-system we are currently using is the green algal group, Volvocales (see our Volvocales Information Project; http://www.unbf.ca/vip). Highly motivated students with interests in either theoretical/genomics or experimental/molecular approaches, and previous research experience are encouraged to apply. Interested applicants should e-mail a CV, summary of research experience and interests, unofficial transcripts, and contact information for three referees to anedelcu@unb.ca.

Applicants should meet the minimum requirements for acceptance in the Biology Department Graduate Program (see http://www2.unb.ca/biology/Degree_Info/Graduate.html).

Heads I win; tails you lose: Evolution News & Views on Gonium, part 2: Model systems and gene duplication

Figure 2 from Hanschen et al. 2016. (a) Predicted number of genes in each phylostratum (PS1–PS9) for Chlamydomonas, Gonium and Volvox. (b) Heatmap of transcription factor abundance for all green algae. Significant over- (+) and under-representation (−) in colonial/multicellular lineages (Gonium and Volvox) is denoted (G test of independence, α=0.05). Rows are clustered (left), an accepted phylogeny is depicted (top). (c) Phylogenetic analysis of gene family evolution. Bars to the left and right of the vertical axis denote the lost and gained gene families respectively, relative to its parental node. (d) Venn diagram of the species distribution of Pfam A domains unique to the volvocine algae.

Figure 2 from Hanschen et al. 2016. (a) Predicted number of genes in each phylostratum (PS1–PS9) for Chlamydomonas, Gonium and Volvox. (b) Heatmap of transcription factor abundance for all green algae. Significant over- (+) and under-representation (−) in colonial/multicellular lineages (Gonium and Volvox) is denoted (G test of independence, α=0.05). Rows are clustered (left), an accepted phylogeny is depicted (top). (c) Phylogenetic analysis of gene family evolution. Bars to the left and right of the vertical axis denote the lost and gained gene families respectively, relative to its parental node. (d) Venn diagram of the species distribution of Pfam A domains unique to the volvocine algae.

Erik Hanschen, the lead author on the Gonium genome paper, is also an old friend of mine from when we were both in Michael Doebeli’s lab at the University of British Columbia. He kindly agreed to write a guest post responding to Evolution News and Views‘ misunderstandings of his paper. Everything below the fold was written by Erik:

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Heads I win; tails you lose: Evolution News & Views on Gonium, part 1

Figure 6 from Hanschen et al. 2016. Multicellularity hinges on the evolution of cell cycle regulation in a multicellular context with subsequent evolution of cellular differentiation (here, cell size-based) and increased body size.

Figure 6 from Hanschen et al. 2016. Multicellularity hinges on the evolution of cell cycle regulation in a multicellular context with subsequent evolution of cellular differentiation (here, cell size-based) and increased body size.

Remember how I said they’re prolific? Before I’ve even had a chance to write up my thoughts on the Gonium genome paperEvolution News & Views has already published theirs. The story has also been picked up by the Washington PostNew HistorianGenNews, and ScienceDaily (that last one looks like just a reprint of the press release from University of the Witwatersrand). By the way, the genome paper is open access, so you don’t need a subscription to see it for yourself.

We already know that cdesign proponentsists are not fans of research into the evolution of multicellularity, and that they have trouble understanding it. In an unsigned article on the Gonium genome at ENV, they admit that

After reading this paper, we’re none the wiser.

That’s too bad. I’m here to help.

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Gonium genome published

Figure 1 from Hanschen et al. 2016. (a) Evolution of cell cycle control (C), expanded ECM (E) and somatic cells (S) are denoted. (b) Micrographs of Chlamydomonas (green; scale bar, 10 μm), Gonium (blue; scale bar, 10 μm) and Volvox (black; scale bar, 25 μm) show morphological differences.

Figure 1 from Hanschen et al. 2016. (a) Evolution of cell cycle control (C), expanded ECM (E) and somatic cells (S) are denoted. (b) Micrographs of Chlamydomonas (green; scale bar, 10 μm), Gonium (blue; scale bar, 10 μm) and Volvox (black; scale bar, 25 μm) show morphological differences.

I haven’t read it yet and won’t have time today, but the Gonium pectorale genome paper just came out in Nature Communications! Erik Hanschen is the lead author, and the article is open access. I previously reported on Erik’s talk at Volvox 2015:

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