(Probably not) Precambrian Volvox

A new(ish) paper in National Science Review evaluates the evidence for various interpretations of Ediacaran microfossils from the Weng’an biota in South China (Xiao et al. 2014. The Weng’an biota and the Ediacaran radiation of multicellular eukaryotes. Natl. Sci. Rev., 1:498–520.). I recommend checking it out; it’s open access, and there’s a lot of interesting stuff in there that I’m not going to address.

These fossils are undoubtedly multicellular, probably eukaryotic, and extremely enigmatic. Their age (582-600 million years) means they could have important implications for the evolution of multicellularity, and their exceptional preservation in great numbers creates the potential for reconstructing their life cycles in great detail. Some of the Weng’an fossils have been interpreted as volvocine algae, an interpretation that I find highly unlikely.

Some of the Weng’an fossils are thought to represent red algae, and this would not be terribly surprising, since red algae have been around for at least 1.2 billion years. Others, for example the tubular fossils, are more problematic, with interpretations as diverse as cyanobacteria, eukaryotic algae, crinoids, and cnidarians.

Fig. 8 from Xiao et al. 2014

Figure 8 from Xiao et al. 2014: Schematic diagram showing diagnostic features of the five recognized species of tubular microfossils in the Weng’an biota.

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Actin evolution in the Volvocales

Kato-Minoura Figure 1

Fig. 1 from Kato-Minoura et al. 2015: Genomic structure of volvocine actin and NAP genes. For comparison, previously identified sequences are also shown. Filled boxes, putative coding exons; open boxes, putative 5′ and 3′ untranslated regions. Intervening sequences are shown by solid lines. Intron positions are indicated by codon and phase numbers with reference to the three alpha-actins of vertebrates (377 amino acids) (Weber and Kabsch 1994). The conserved intron positions are linked with dotted lines. ATG, translation start codon; TAA or TGA, stop codon.

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African Volvox in Montana

Ninepipe Reservoir

Ninepipe Reservoir near Charlo, MT. Photo by Aeravi.

Last summer, I hosted Drs. Hisayoshi Nozaki, Noriko Ueki, Osami Misumi, and two graduate students from the University of Tokyo, Kayoko Yamamoto and Shota Yamashita, to collect volvocine algae from Montana lakes. To our surprise, we found a species of Volvox (V. capensis) that had previously only ever been found in South Africa! Dr. Nozaki’s team identified the algae collected in Ninepipe Reservoir based on their morphology and DNA sequencing. South Africa and Montana: this is about as disjunct as a distribution can be. Is Volvox capensis a master of long-distance dispersal? Is its distribution actually cosmopolitan, and if so, why hasn’t it ever been found anywhere else?

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Expression and form: Arash Kianianmomeni on gene regulation

Kianianmomeni Figure 1

Figure 1 from Kianianmomeni 2015. Gene regulatory mechanisms behind the evolution of multicellularity. Model illustrating the role of gene regulatory mechanisms in the evolution of multicellular Volvox from a Chlamydomonas-like ancestor.

Arash Kianianmomeni’s latest paper in Communicative & Integrative Biology addresses the possible roles of gene regulation and alternative splicing in the evolution of multicellularity and cellular differentiation (Kianianmomeni, A. 2015. Potential impact of gene regulatory mechanisms on the evolution of multicellularity in the volvocine algae. Commun. Integr. Biol., 37–41. doi 10.1080/19420889.2015.1017175). The article is an ‘Addendum’ to a 2014 study by Kianianmomeni and colleagues in BMC Genomics. Communicative & Integrative Biology often invites authors to write these addenda after they have published a (usually high impact) paper elsewhere, providing authors the opportunity to publish material that was not included in the original paper due to space limitations or because it was opinionated or speculative. I may address the BMC Genomics article in a future post, but right now there is more new volvocine research than I have time to write about (it should be an exciting Volvox meeting this summer!).

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Pierrick Bourrat on levels, time, and fitness, part 2: collective fitness

Last week, I posted some thoughts on Pierrick Bourrat’s new paper in Philosophy and Theory in Biology, focusing on his criticism of Rick Michod’s ‘export of fitness’ framework. This week, I’ll take a look at the second of Bourrat’s criticisms, regarding the transition from MLS1 to MLS2, as first defined by Damuth & Heisler, during a transition in individuality.
MLS1 and MLS2 refer to two different versions of MultiLevel Selection. As Bourrat describes it (and this is pretty much in line with other authors), fitness in MLS1 is defined in terms of the number of particles (or lower-level units, or cells) produced, while in MLS2 the fitnesses of the particles and collectives (or cells and multicellular organisms) are measured in different units. Cell-level fitness (for example) is defined in terms of the number of daughter cells, organism-level fitness is based on the number of daughter organisms. (As with last week’s post, I’ll generally stick to cells and organisms, though the principles apply equally to any two adjacent levels.

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Volvox, the…game?

The Steam Greenlight Community has announced the development of Volvox (warning: autoplay video), a puzzle game with the goal of building “the first pluricellular beings.” Written by three students and former students of Italy’s Politecnico di Milano, the game features triangular cells called Trimoebas that roll around under the player’s control and gain abilities as the game progresses. The team, which forms Neotenia, Ltd., won the Italian national competition and is a semifinalist for the 2015 Microsoft Imagine Cup. The first fifteen levels are available as a free Unity WebGL Demo (takes a while to load).
The game reminds me a bit of Lemmings or Lode Runner in its simplicity and focus on solving deceptively simple tasks. It looks good, with a sort of hand-drawn, colored pencil, pastel look. Each trimoeba has an eye that mostly follows the mouse pointer, although they get bored and start looking around if it doesn’t move for a few seconds. Powers (at least those that exist in the demo) are indicated by the affected side of the triangle being colored; for example, blue sides can’t be stuck in glue. The documentation is a little thin right now, and it took me a while to figure out what was expected on the second level.

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Pierrick Bourrat on levels, time, and fitness, part 1: zero fitness?

Pierrick Bourrat’s new paper in Philosophy and Theory in Biology criticizes aspects of the influential ‘export of fitness’ framework developed by Rick Michod and colleagues and extended by Samir Okasha (Bourrat, P. 2015. Levels, time and fitness in evolutionary transitions in individuality. Philos. Theory Biol., 7: e601. doi: 10.3998/ptb.6959004.0007.001). According to this view, an evolutionary transition in individuality, for example from unicellular to multicellular life, involves a transfer of fitness from the lower level units (e.g. cells) to the higher level unit (e.g. nascent multicellular organism). Fitness is defined as the product of viability and fecundity, and the emergence of a division of labor between reproductive (germ) and non-reproductive (somatic) units at the lower level exports fitness to the higher level. Full disclosure: Rick Michod was my Ph.D. co-advisor, and he has had a huge influence on my thinking about this topic.

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Who are you calling lower?

Weismann Fig. 62

Fig. 62 from Weismann, A. 1904. The Evolution Theory. London: Edward Arnold. Pandorina morum; after Pringsheim. I, A young colony, consisting of 16 cells. II, Another colony, whose cells have reproduced daughter-colonies; all the cells uniformly alike. III, A young Volvox-colony; sz, somatic cells; kz, germ-cells.

I needed to cite some information from August Weismann’s 1904 book The Evolution Theory1 yesterday, so I did something I rarely do anymore: walked over to the library and checked out a physical copy. The University of Montana library has a first edition, two-volume set of the translation by Arthur Thomson. I’m always interested to see how biologists thought about Volvox before people like Richard Starr, David Kirk, and Rüdiger Schmitt came on the scene. All of the quoted text is from pages 257-261 in Volume I.
Among the lower Algae there is a family, the Volvocinæ, in which the differentiation of the many-celled body on the principle of division of labour has just set in; in some genera it has been actually effected, though in the simplest way imaginable, and in others it has not yet begun.

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Evolutionary Transitions to Multicellular Life published

Iñaki Ruiz-Trillo and Aurora Nedelcu have recently edited a new book on the evolution of multicellularity, Evolutionary Transitions to Multicellular Life.  The 22 chapters are divided into five sections: “Multicellularity in the Tree of Life,” “Model-Systems,” “Theoretical Approaches,” “Genomics Insights,” and “Molecular Mechanisms,” and the forward is written by Nicole King. Volvox  shows up in the chapters by Susan C. Sharpe, Laura Eme, Matthew W. Brown and Andrew Roger (“Timing the origins of multicellular eukaryotes through phylogenomics and relaxed molecular clock analyses”); by myself and Aurora Nedelcu (“Volvocine algae: from simple to complex multicellularity”); by Cristian A. Solari, Vanina J. Galzenati and John O. Kessler (“The evolutionary ecology of multicellularity: the volvocine green algae as a case study”); by John O. Kessler, Aurora M. Nedelcu, Cristian A. Solari and Deborah E. Shelton (“Cells acting as lenses: a possible role for light in the evolution of morphological asymmetry in the volvocine algae”); and by Daniel Lang and Stefan A. Rensing (“The evolution of transcriptional regulation in the Viridiplantae and its correlation with morphological complexity”).

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