New review of green algal sex

Hiroyuki Sekimoto from Japan Women’s University has published a review of sexual reproduction in the volvocine algae and in the Charophyte Closterium in the Journal of Plant Research. In addition to a brief description of the Chlamydomonas sexual cycle, it includes a succinct review of the genetics of sex and sex determination. Unfortunately, the article is paywalled, and my inquiry to the author has so far gone unanswered.

Figure 1 from Sekimoto 2017. The life cycle of Chlamydomonas reinhardtii. Vegetative cells (V) di erentiate into mt+ and mt− gametes (G) during nitrogen starvation (−N). Mating types are restricted by mating-type loci (+ and −). When gametes are mixed, the plus and minus agglutinin mol- ecules on their agellar surfaces adhere to each other, and this adhe- sion results in increased intracellular cAMP levels. The signal trig- gers gamete cell wall release and mating-structure activation. Cells then fuse to form binucleate quadri agellated cells. Zygotes with thick cell walls germinate in response to light and nitrogen supple- mentation, and undergo meiosis to release four haploid vegetative cells

Figure 1 from Sekimoto 2017. The life cycle of Chlamydomonas reinhardtii. Vegetative cells (V) differentiate into mt+ and mt− gametes (G) during nitrogen starvation (−N). Mating types are restricted by mating-type loci (+ and −). When gametes are mixed, the plus and minus agglutinin molecules on their flagellar surfaces adhere to each other, and this adhesion results in increased intracellular cAMP levels. The signal triggers gamete cell wall release and mating-structure activation. Cells then fuse to form binucleate quadriflagellated cells. Zygotes with thick cell walls germinate in response to light and nitrogen supplementation, and undergo meiosis to release four haploid vegetative cells.

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Convergence falsifies evolution, according to Cornelius Hunter

Xerus princeps

Xerus princeps, the mountain ground squirrel.

Before I saw the light and switched to studying Volvox, I studied squirrels. With apologies to Iris Vander Pluym, squirrels are cool. If you grew up in the squirrel-deprived eastern U.S., you might not realize that there are over a hundred species. Chipmunks are squirrels. Marmots are fat squirrels. Prairie dogs are adorable squirrels.

Most of my squirrel work, and some of my Volvox work, has focused on understanding the evolutionary relationships among species. This fits in the subfield of evolutionary biology known as phylogenetics. Phylogenetics results are often visualized as trees and published in journals like Cladistics, Molecular Phylogenetics and Evolution, and Systematic Biology. Phylogenetics is a vast subfield, with a huge number of papers devoted to developing methods that are theoretically and empirically sound.

Cornelius Hunter understands none of this. In a recent post over at Evolution News and Science Today (which used to be Evolution News and Views…when did that change?), he argues against the whole idea of common descent, the very foundation of phylogenetics. Dr. Hunter argues that convergence, similarities among distantly related species, falsifies evolution. The nature of his arguments shows pretty conclusively that he doesn’t understand the basic logic of what he’s criticizing.

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Rediscovered after two thirds of a century: Pleodorina sphaerica

Pleodorina sphaerica

Figure 1 from Nozaki et al. 2017. Pleodorina sphaerica.

There really aren’t enough people looking for volvocine algae. There’s a suspicious tendency for the geographical centers of volvocine diversity — southern Africa, central North America, southeast Asia — to include the home institutions of phycologists studying volvocine diversity — Mary Pocock, Richard Starr, Hisayoshi Nozaki, respectively. I find it much more likely that this is an artifact of sampling effort than that, for example, central Africa and Central and South America are depauperate of volvocine algae.

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Look what came in the mail yesterday!

Biological Individuality

A project started five years ago has finally borne fruit. In May, 2012 I joined a group of philosophers, historians, and biologists in Philadelphia for the Cain Conference “E pluribus unum: Bringing biological parts and wholes into historical and philosophical perspective.” The meeting was organized by Lynn Nyhart and Scott Lidgard, with the goal

…to pursue the question: How can historians, philosophers, and biologists help each other to understand part-whole relationships in biology, both today and in the past?

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Volvox 2017: one week left for early registration

Volvox 2017 LogoJust what the headline says: early registration for The Fourth International Volvox Conference ends May 19th. After that, prices go up $100 for everybody. The registration fees sound a bit steep (up to $650), but when you consider that they include meals, lodging, and transportation between the hotel and the conference, they’re not bad at all:

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Devolution isn’t a thing

Devo

Yesterday I volunteered as a Meeting Mentor at the AbSciCon meeting. It’s not a big commitment; essentially all you have to do is hang out with a high school student for half a day, going to talks and enjoying the meeting as you normally would.

During a break, I was chatting with my mentee about Betül Kaçar’s research, and he surprised me by pointing out that (as he put it), “Devolution isn’t a thing.” The student I was paired with is interested in physics and space exploration, but his comment showed an insight that not even all professional biologists really own. From what I’ve seen, it’s an insight that very few creationists own.

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New fossil proves plants are younger than previously thought

That’s not a headline you’re likely to see again. Hopefully it made you think something along the lines of “how does that work, exactly?” Because it doesn’t. If your estimate of the age of a taxon is based on its oldest known fossil, finding a newer fossil isn’t likely to change that estimate. If it’s an extinct group, a newer fossil might show that it stuck around later than you thought, but not that it originated later. Paleontologists recognize that fossil-based estimates of ages are almost always underestimates, since the fossil record is spotty (and generally spottier the further back you go).

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J. S. Huxley part 2: Volvox

Last time, I wrote about Julian Huxley’s 1912 book, The Individual in the Animal Kingdom, and his use of the volvocine algae as an example. I liked most of what he had to say, though I took issue with his assertion that

…all the other members of the family except Volvox…are colonies and nothing more—their members have united together because of certain benefits resulting from mere aggregation, but are not in any way interdependent, so that the wholes are scarcely more than the sum of their parts.

This is, of course, a matter of how we define a multicellular organism, but I think any definition that excludes, for example, Eudorina, is not a very useful one.

This time, I’ll look at the rest of what Huxley had to say about the volvocine algae, most of which is about Volvox:

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J. S. Huxley part 1: Gonium

Julian Huxley was one of the biologists responsible for the merging of Mendelian genetics and Darwinian evolution in the early 20th century, the modern synthesis. His most influential work was Evolution: The Modern Synthesis, published in 1942. Thirty years earlier, though, he published a book on biological individuality, The Individual in the Animal Kingdom. Thankfully, the copyright on this book has expired, so it is now part of the public domain, and a scanned version is available for free in pdf and epub versions from Google.

Huxley Cover

Any book with Volvox on the cover can’t be all bad!

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