I’m a junior author on a new paper from Erik Hanschen and colleagues, “Multicellularity drives the evolution of sexual traits.”
New paper in The American Naturalist
Category: Papers
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
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.
Pleodorina sphaerica paper published in Phycologia
Figures 1-9 from Nozaki et al. 2017. Pleodorina sphaerica.
Pleodorina sphaerica Iyengar was considered to be a phylogenetic link between Volvox and the type species Pleodorina californica Shaw because it has small somatic cells distributed from the anterior to posterior poles in 64- or 128-celled vegetative colonies. However, cultural studies and molecular and ultrastructural data are lacking in P. sphaerica, and this species has not been recorded since 1951. Here, we performed light and electron microscopy and molecular phylogeny of P. sphaerica based on newly established culture strains originating from Thailand. Morphological features of the present Thai species agreed well with those of the previous studies of the Indian material of P. sphaerica and with those of the current concept of the advanced members of the Volvocaceae. The present P. sphaerica strains exhibited homothallic sexuality; male and facultative female colonies developed within a single clonal culture. Chloroplast multigene phylogeny demonstrated that P. sphaerica was sister to two other species of Pleodorina (P. californica and Pleodorina japonica Nozaki) without posterior somatic cells, and these three species of Pleodorina formed a robust clade, which was positioned distally in the large monophyletic group including nine taxa of Volvox sect. Merrillosphaera and Volvox (sect. Janetosphaera) aureus Ehrenberg. Based on the present phylogenetic results, evolutionary losses of posterior somatic cells might have occurred in the ancestor of P. californica and P. japonica. Thus, P. sphaerica might represent an ancestral morphology of Pleodorina, rather than of Volvox.
Nozaki, H., W. Mahakham, S. Athibai, K. Yamamoto, M. Takusagawa, O. Misumi, M. D. Herron, F. Rosenzweig, M. Kawachi. 2017. Rediscovery of the species of “ancestral Volvox”: morphology and phylogenetic position of Pleodorina sphaerica (Volvocales, Chlorophyceae) from Thailand. Phycologia 56:469–475. doi: 10.2216/17-3.1
Philosophy of Science article online early
My new article “Fitness and individuality in complex life cycles” is available as “Just accepted” at Philosophy of Science. I presented an early version of this paper in a symposium organized by Maureen O’Malley, Peter Godfrey-Smith, and James Griesemer at the Philosophy of Science Association Meeting in Chicago two years ago.