Tag: Multicellularity

Posted on
by

With the permission of the publisher and the authors, we have made internally peer-reviewed but unformatted drafts of all 18 chapters of The Evolution of Multicellularity available for download. Please note that there may be substantive differences between these pre-publication versions and the final book chapters.

The full book is available on Amazon and direct from the publisher in hardcover and ebook formats. The paperback is due out in 12-18 months, at which point the price of the ebook will drop.

Continue reading →

Posted on
by

The Evolution of Multicellularity, co-edited with Peter Conlin and Will Ratcliff, has been published by CRC Press. It’s available on Amazon, but cheaper to order direct, and for the time being you can save 20% with discount code FLA22 (I don’t know how long that will last).

The goal of this book is to provide an overview of the evolution of multicellularity: the types of multicellular groups that exist, their evolutionary relationships, the processes that led to their origins and subsequent evolution, and the conceptual frameworks in which their evolution is understood. In four main sections, the contributors review the philosophical issues and theoretical approaches to understanding the evolution of multicellularity, the evolution of aggregative multicellularity, the evolution of clonal multicellularity, and the evolution of multicellular life cycles and development. While the subject is too broad to cover in a truly comprehensive way, the contributors have done an outstanding job of synthesizing the critical information on their respective topics. We hope that this book will serve as a starting point for readers interested in the evolution of multicellularity, a reference for researchers on the subject, and a jumping-off point to stimulate future research.

The publisher has put pretty strict limits on what we can share (they want to sell books, after all), so I won’t be posting a downloadable version (I don’t, in fact, have one). However, the Foreword and Chapter 1 (together) can be downloaded for free, and some of the authors posted preprints of their chapters (which the publisher allowed). I have linked to these in the table of contents below. If I learn of others, I’ll update this post.

I’m biased, of course, but I really do think the authors have done an outstanding job with their respective chapters. I hope you think so, too!

Continue reading →

Posted on
by

Jim Umen and I have published an article in the newest issue of Annual Review of Genetics. We review some green algae that are or have the potential to be models for the evolution of multicellularity, including Volvox, Ulva, Chara, and Caulerpa. Transitions from unicellular to multicellular (or, in the case of Caulerpa, giant, multinucleate unicellular) have been frequent and varied within the green algae, and we argue that studying diverse examples is necessary to understand how and why these transitions have taken place.

Abstract:

The repeated evolution of multicellularity across the tree of life has profoundly affected the ecology and evolution of nearly all life on Earth. Many of these origins were in different groups of photosynthetic eukaryotes, or algae. Here, we review the evolution and genetics of multicellularity in several groups of green algae, which include the closest relatives of land plants. These include millimeter-scale, motile spheroids of up to 50,000 cells in the volvocine algae; decimeter-scale seaweeds in the genus Ulva (sea lettuce); and very plantlike, meter-scale freshwater algae in the genus Chara (stoneworts). We also describe algae in the genus Caulerpa, which are giant, multinucleate, morphologically complex single cells. In each case, we review the life cycle, phylogeny, and genetics of traits relevant to the evolution of multicellularity, and genetic and genomic resources available for the group in question. Finally, we suggest routes toward developing these groups as model organisms for the evolution of multicellularity.

Umen, J. & M.D. Herron. 2021. Green algal models for multicellularity. Annual Review of Genetics  55:603-632. doi: 10.1146/annurev-genet-032321-091533 Free e-print

Posted on
by

Postdoc Kimberly Chen has published a lay summary of our recent Scientific Reports paper, in which we showed that predation can drive the evolution of multicellularity in the green alga Chlamydomonas:

Multicellular life is one of the most astonishing wonders on Earth, but why and how does it arise in the first place, and at what cost? To help answer these questions, we exposed single-celled algae to predators and watched them evolve into multicellular life. Within a year, they had formed groups of cells to avoid being eaten – but at a price.

Chen, I-C. K. & M. D. Herron. 2019. Predators drive the evolution of multicellularity. The Science Breaker 257. doi: 10.25250/thescbr.brk257

Posted on
by

A new paper describing the results of a microbial evolution experiment has been published in Scientific Reports. Predation by the filter-feeding predator Paramecium tetraurelia drove the evolution of simple multicellular structures in the green alga Chlamydomonas reinhardtii:

Herron et al. 2019 Fig. 2
Figure 2 from Herron et al. 2019. Depiction of C. reinhardtii life cycles following evolution with (B2, B5) or without (K1) predators for 50 weeks. Categories (A–D) show a variety of life cycle characteristics, from unicellular to various multicellular forms. Briefly, A shows the ancestral, wild-type life cycle; in B this is modified with cells embedded in an extracellular matrix; C is similar to B but forms much larger multicellular structures; while D shows a fully multicellular life cycle in which multicellular clusters release multicellular propagules. Representative microscopic images of each life cycle category are at the bottom (Depicted strain in boldface).

From the abstract:

Here we show that de novo origins of simple multicellularity can evolve in response to predation. We subjected outcrossed populations of the unicellular green alga Chlamydomonas reinhardtii to selection by the filter-feeding predator Paramecium tetraurelia. Two of five experimental populations evolved multicellular structures not observed in unselected control populations within ~750 asexual generations. Considerable variation exists in the evolved multicellular life cycles, with both cell number and propagule size varying among isolates. survival assays show that evolved multicellular traits provide effective protection against predation. These results support the hypothesis that selection imposed by predators may have played a role in some origins of multicellularity.

Herron MD, Borin JM, Boswell JC, Walker J, Knox CA, Boyd M, Rosenzweig F, Ratcliff WC. 2019 De novo origins of multicellularity in response to predation. Sci. Rep. 9, 2328. (doi: 10.1038/s41598-019-39558-8)

Posted on
by

The paper describing the genetics of the multicellular Chlamydomonas reinhardtii strain that evolved in response to selection on settling rate is published in Royal Society Open Science:

Figure 3 from Herron et al. 2018. Results of phylostratigraphy analysis of differentially expressed genes. The y-axis represents the log odds of the observed degree of over/underrepresentation relative to genome-wide frequencies. The Bonferroni-corrected p-values result from a hypergeometric test (α = 0.0025, equivalent to a false discovery rate of 1%) performed in GeneMerge v. 1.4. ‘n.s.’, not significant.

Continue reading →

Posted on
by
Pennisi figure
Top left: Chlamydomonas (Andrew Syred/Science Source). Top right: Gonium (Frank Fox/ Science Photo Library). Bottom: Volvox (Wim van Egmond/Science Photo Library).

A news item by Elizabeth Pennisi in Science mentions our work experimentally evolving multicellularity in Chlamydomonas reinhardtii:

[Will Ratcliff’s snowflake] yeast results weren’t a fluke. In 2014, Ratcliff and his colleagues applied the same kind of selection for larger cells to Chlamydomonas, the single-celled alga, and again saw colonies quickly emerge. To address criticism that his artificial selection technique was too contrived, he and Herron then repeated the Chlamydomonas experiment with a more natural selective pressure: a population of paramecia that eat Chlamydomonas—and tend to pick off the smaller cells. Again a kind of multicellularity was quick to appear: Within 750 generations—about a year—two of five experimental populations had started to form and reproduce as groups, the team wrote on 12 January in a preprint on bioRxiv.

Posted on
by

PLoS ONE

Figure 8 from Boyd et al. 2018
Figure 8 from Boyd et al. 2018. Analysis of algal movement due to light exposure where positive values indicate movement toward the light source and negative values indicate movement away from the light source.

Former undergraduate researcher Maggie Boyd has published her analysis of motility in experimentally evolved Chlamydomonas reinhardtii in PLoS ONE:

C. reinhardtii is capable of photosynthesis, and possesses an eyespot and two flagella with which it moves towards or away from light in order to optimize input of radiant energy. Motility contributes to C. reinhardtii fitness because it allows cells or colonies to achieve this optimum. Utilizing phototaxis to assay motility, we determined that newly evolved multicellular strains do not exhibit significant directional movement, even though the flagellae of their constituent unicells are present and active. In C. reinhardtii the first steps towards multicellularity in response to predation appear to result in a trade-off between motility and differential survivorship, a trade-off that must be overcome by further genetic change to ensure long-term success of the new multicellular organism.

Maggie is now a Ph.D. student in Northwestern University’s Biomedical Engineering program.

Boyd, M., Rosenzweig, F. and Herron, M.D. 2018. Analysis of motility in multicellular Chlamydomonas reinhardtii evolved under predation. PLoS ONE, 13: e0192184. doi: 10.1371/journal.pone.0192184