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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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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Ann Gauger teaches us about Volvox, part 2

Last time, I criticized Ann Gauger’s Evolution News and Views article “A Simple Transition to Multicellularity — Not!” for asserting that the requirement for kinesins in Volvox inversion implied a requirement for novel genes in the evolution of multicellularity. In a similar vein, Dr. Gauger presents programmed cell death and sex as problems for this transition:
The somatic cells commit suicide by a process known as apoptosis — programmed cell death — that I wrote about here. This process involves a minimum of several novel genes as well.
Where does this assertion that programmed cell death in Volvox “involves a minimum of several novel genes” come from? Programmed cell death (PCD) occurs in many unicellular eukaryotes, including Chlamydomonas reinhardtii. Furthermore, two types of metacaspases, genes involved in PCD in many algae and plants, are found in both Chlamydomonas and Volvox.

Partial alignment of representative type I and type II metacaspase predicted sequences from red algae (Porphyra yezoensis; Py), green algae (Chlamydomonas reinhardtii, Cr; Volvox carteri, Vc), vascular plants (Arabidopsis thaliana; At), excavates (Trypanosoma cruzi, Tc; Leishmania braziliensis, Lb), diatoms (Thalassiosira pseudonana, Tp; Phaeodactylum tricornutum, Pt), haptophytes (Emiliania huxleyi; Eh), pelagophytes (Auroecoccus anaphagefferens; Aa), yeasts (Schizosaccharomyces pombe, Sp; Saccharomyces cerevisiae, Sc) showing the conservation of the cysteine-histidine dyad and the insertion characteristic of plant type II metacaspases. From Nedelcu, A.M. 2009. Comparative genomics of phylogenetically diverse unicellular eukaryotes provide new insights into the genetic basis for the evolution of the programmed cell death machinery. J. Mol. Evol., 68: 256–268. doi 10.1007/s00239-009-9201-1.

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Ann Gauger teaches us about Volvox, part 1

Over at Evolution News and Views (ENV), the blog for the Discovery Institute, Ann Gauger has a new article about Volvox (“A Simple Transition to Multicellularity — Not!”). This isn’t the first time ENV has weighed in on the evolution of multicellularity (see here and here, for example), but since their website doesn’t allow comments, this is the first time I’ve had a platform from which to respond.
The article starts out with a mostly accurate description of Volvox biology, although the description as
…among the simplest animals to have more than one cell type

is cringe-worthy: Volvox is no more an animal than is a tomato:


An accurate, if low-resolution, phylogeny.

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