Registration and abstract submission are open for the 70th Annual Meeting of the Phycological Society of America, July 24-30 at John Carroll University in Cleveland, Ohio. The tentative schedule is here.
Fig. 1 from Herron 2016. Examples of volvocine species. A: Chlamydomonas reinhardtii, B: Gonium pectorale, C: Astrephomene gubernaculiferum, D: Pandorina morum, E: Volvulina compacta, F: Platydorina caudata, G: Yamagishiella unicocca, H: Colemanosphaera charkowiensis, I: Eudorina elegans, J: Pleodorina starrii, K: Volvox barberi, L: Volvox ovalis, M: Volvox gigas, N: Volvox aureus, O: Volvox carteri. A and B by Deborah Shelton.
The meeting review for the Third International Volvox Conference is now available online at Molecular Ecology (doi: 10.1111/mec.13551). The editors warned me ahead of time that the challenge for this paper would be to make it of broad interest to the readership of Molecular Ecology, so there is a lot of background information that will be old news to members of the Volvox community.
Volvox africanus (from Herron et al. 2010)
The worst-kept secret among Volvox researchers is that the current volvocine taxonomy is a train wreck. Within the largest family, the Volvocaceae, five nominal genera are polyphyletic (Pandorina, Volvulina, Eudorina, Pleodorina, and Volvox). Of the remaining three, two are monotypic (Platydorina and Yamagishiella). Only the newly described Colemanosphaera is monophyletic with more than one species. The extent of the problem was suspected long before it was confirmed by molecular phylogenetics, and ad hoc attempts to deal with it have led to the existence of such taxonomic abominations as ‘sections,’ ‘formas,’ and ‘syngens.’ An overhaul is called for, but it is complicated by the aforementioned loss of type cultures.
In a session chaired by Ray Goldstein, we heard about recent advances in the biophysics of Volvox and Chlamydomonas. Over the last decade or so, Volvox has proven to be an experimentally tractable model system for several questions in hydrodynamics and flagellar motility. Volvox colonies can be grown in large numbers (even by physicists!), clonal cultures have relatively little among-colony variation, and they are large enough to be manipulated in ways that most single-celled organisms can’t. Furthermore, their simple structure accommodates the kind of simplifying assumptions physicists are fond of, leading Kirsty Wan (among others at the meeting) to refer to them as “spherical cows.”
In a series of papers, Douglas Brumley and colleagues have explored flagellar dynamics in Volvox carteri. Amazingly, these studies have shown that the synchronized beating of V. carteri‘s ~1000 pairs of flagella is entirely due to hydrodynamic coupling. In other words, in spite of the apparent high degree of coordination among the flagella of separate cells within a colony, no actual coordination among cells takes place. Synchronization emerges from indirect interactions mediated by the liquid medium. An elegant demonstration of this is shown in Brumley et al.’s 2014 eLife paper, in which somatic cells were physically separated from a colony and held at various distances from each other. Despite there being no direct physical connection between the cells, they beat synchronously when close together, with a phase shift that increased with increasing cell to cell distance:
This is taking much longer than I ever expected; hopefully I can get through blogging about Volvox 2015 before registration opens for Volvox 2017!
The final session on day 1 (August 20) was chaired by Aurora Nedelcu from the University of New Brunswick. Dr. Nedelcu’s introduction emphasized some of the basic questions in evolutionary biology, aside from the origins of multicellularity and sex, on which volvocine research has provided insights: the evolution of morphological innovations, the relative importance of cis-regulatory changes vs. protein-coding changes, kin vs. group selection as competing explanations for the evolution of altruism, the evolution of soma and of indivisibility, the genetic basis of cellular differentiation, and the role of antagonistic pleiotropy (my hastily scribbled notes seem to say “antagonistic pleiotropy of olsl.” Is that supposed to be rls1? This is the cost of waiting too long to write. Maybe Aurora can clarify.).
Ray Goldstein‘s working (!) replica of Antonie van Leeuwenhoek’s microscope.
At the start of the Development session, I asked for a show of hands of people who self-identify as developmental biologists. About four went up. That’s not quite fair, since there’s some ambiguity in the question (primarily? exclusively?), but my point was that what all of us who are interested in the evolution of multicellularity study is the evolution of development. In fact, it might fairly be said that the origin of multicellularity is the origin of development.
When I was a senior in high school, I gave my friend Arthur Malpere a ride to school in my ’77 MGB just about every day (well, every day it was running). I had a cassette of the then fairly new Licensed to Ill, and Art insisted that we listen to it every damn day. The ride to school was on the order of ten minutes, so we would listen to ten minutes on the way to school, then pick up where we left off, usually mid-song, on the way home (for those of you too young to remember cassettes, it wasn’t trivial to return to the beginning of a song). Of all the outstanding songs on that album, possibly my favorite was “Paul Revere,” a sort of old-west style automythology of the band’s origin (in spite of the casual misogyny, I still do like it pretty well).
One of the most studied aspects of Volvox development is the differentiation of its 2000 or so cells into two types: a few (usually 12-16) large reproductive cells (germ) and the rest small, biflagellate cells that provide motility (soma). The main genes controlling this differentiation have long been known, but the details of how they work are still being worked out.
Erik Hanschen (left) with Cristian Solari, David Smith, and Jillian Walker
We spent Wednesday afternoon sampling some ponds around Cambridge, looking for Volvox and related algae. Dr. Hisayoshi Nozaki, whose lab has described a substantial proportion of the known species, led the effort, but somehow we failed to locate our quarry.
Thomas Pröschold checking an algae-filled pond.
I believe that sex is one of the most beautiful, natural, wholesome things that money can buy.
–Steve Martin
Volvox, and the volvocine algae in general, are well known as a model system for the evolution of multicellularity and cellular differentiation, but they are also an outstanding model for the evolution of sex and mating types. Volvocine algae are facultatively sexual, with haploid vegetative colonies reproducing asexually through mitosis but occasionally entering a sexual cycle that usually results in a diploid, desiccation-resistant zygote or ‘spore.’ Most of the small colonial species and unicellular relatives are isogamous, that is, the gametes are of equal size. Nevertheless, each species has two self-incompatible mating types, usually designated as ‘plus’ and ‘minus.’ In some of the larger species, the gametes have diverged into a small, motile form that we call sperm and a large, often immotile form that we call eggs. Across the eukaryotic domain, it is gamete size, not form of genitalia, fancy plumage, or receding hairline, that define males and females.
The volvocine algae span a wide range of mating systems, making them a useful (and I think underutilized) system for comparative studies of the evolution of sex. As I’ve already mentioned, both isogamous (equal-sized gametes) and oogamous (sperm and eggs) species exist, and there is good reason to suspect that oogamy has evolved independently in two separate lineages:
Isogamy and oogamy (Kirk 2006. Curr. Biol., 16:R1028.)