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:
New paper in Royal Society Open Science
New paper in The American Naturalist
I’m a junior author on a new paper from Erik Hanschen and colleagues, “Multicellularity drives the evolution of sexual traits.”
Chlamydomonas multicellularity work mentioned in Science
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.
Evolution Digest on self-fertilization
Alan M. Vincent has written an Evolution Digest about our recent paper on the evolution of outcrossing versus selfing in the volvocine algae (“Going solo: Self‐fertilization in haploid algae may not lead to evolutionary decline“):
Many traits are considered evolutionary dead‐ends when comparing the short‐term advantage for an individual against long‐term detrimental effects on lineage persistence. It is fairly rare, however, for these claims to be tested. For example, it is assumed that specialization increases rates of extinction. Day et al. (2016) used similar phylogenetic methods to Hanschen et al. (2017) to test whether specialization led to increased extinction rates in ten phylogenies of various plants, insects, flatworms and birds. They found that specialization was less detrimental than expected: only two phylogenies showed significant reduction in diversification and higher “tippiness.” Similarly, Hanschen et al. (2017) show that selfing did not seem to be a dead‐end trait (corroborated by the two reversals from selfing to outcrossing).
New paper in PLoS ONE
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
Commentary on self-fertilization and outcrossing by Erik Hanschen
The lead author of the recent Evolution paper has posted a commentary on kudos that includes some ideas not included in the paper:
The life cycle and ecology of volvocine algae may be key to understanding the long-term persistence of self-fertilization. First, selfing in homothallic volvocine algae is facultative; in a genetically diverse population, most matings will be between genetically distinct strains. Second, volvocine algae have a haploid-dominant life cycle with a metabolically active, multicellular haploid stage and a dormant, unicellular diploid stage. Inbreeding depression may thus be less important than in species with diploid-dominant life cycles. Finally, the dormant diploid stage allows volvocine algae to overwinter, meaning that the ability to self-fertilize is crucial for the survival of colonists to new ponds. Thus facultative selfing might provide volvocine algae with the benefits of outcrossing (when other genotypes are around) without the cost of potentially being unable to find a mate.
New paper in Evolution
Hanschen ER, Herron MD, Wiens JJ, Nozaki H, Michod RE. 2017. Repeated evolution and reversibility of self-fertilization in the volvocine green algae. Evolution (pdf)
New paper in Philosophical Transactions B
Ratcliff WC, Herron MD, Libby E, Conlin PL. 2017. Nascent life cycles and the emergence of higher-level individuality. Philos. Trans. R. Soc. B Biol. Sci. 372, 20160420. (doi:10.1098/rstb.2016.0420)
Congratulations to Jacob Boswell: SSB grant funded!
Graduate student Jacob Boswell got the word yesterday that his Society of Systematic Biologists Graduate Student Research Award will be funded. The award will support his sequencing of cDNA from various volvocine species for multi-gene phylogenetic reconstructions.
New book chapter on biological individuality
Herron, M. D. 2017. Cells , colonies, and clones: individuality in the volvocine algae. In S. Lidgard & L. K. Nyhart, eds., Biological Individuality: Integrating Scientific, Philosophical, and Historical Perspectives (pp. 63–83). University of Chicago Press, Chicago.