Why don’t we revise volvocine taxonomy?

Volvocine taxonomy is in a sorry state. Most nominal genera, and some nominal species, are almost certainly polyphyletic. More than once, I’ve been asked during a talk, “Why is Volvox scattered all over the tree?”

JPhycol2010Fig2a

Fig. 2A from Herron et al. 2010. The traits characteristic of the genus Volvox—asexual forms with >500 cells, only a few of which are reproductive, and oogamy in sexual reproduction—have arisen at least three times independently: once in the section Volvox (represented by V. globator, V. barberi, and V. rousseletii), once in V. gigas, and once or possibly twice in the remaining Volvox species. Branch shading indicates maximum-parsimony reconstruction (white = absent, black = present, dashed = ambiguous). Pie charts indicate Bayesian posterior probabilities at selected nodes. Numbers to the left of cladograms indicate log-Bayes factors at selected nodes: positive = support for trait presence, negative = support for trait absence. Interpretation of log-Bayes factors is based on Kass and Raftery’s (1995) modification of Jeffreys (1961, Theory of probability. 3rd edn. Oxford Univ. Press, Oxford, UK.): 0 to 2, barely worth mentioning; 2 to 6, positive; 6 to 10, strong; >10, very strong. Boldface numbers following species names indicate Volvox developmental programs following Desnitski (1995).

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Best rejection letter ever, or science urban legend?

Antonie van Leeuwenhoek by Jan Verkolje. Public domain image from Wikimedia Commons.

Antonie van Leeuwenhoek by Jan Verkolje. Public domain image from Wikimedia Commons.

Trying to find some background on Van Leeuwenhoek’s discovery of Volvox, I came across the following on Wikipedia:

Despite the initial success of Van Leeuwenhoek’s relationship with the Royal Society, this relationship was soon severely strained. In 1676, his credibility was questioned when he sent the Royal Society a copy of his first observations of microscopic single-celled organisms. Previously, the existence of single-celled organisms was entirely unknown. Thus, even with his established reputation with the Royal Society as a reliable observer, his observations of microscopic life were initially met with both skepticism and open ridicule.[12]

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In which I agree with Uncommon Descent

BizarroWorld

We’re both fans of Betul Kacar‘s research (see “AbSciCon day 3: the tape of life“). I know why I like it, but I can’t quite figure out why they do. Dr. Kacar’s research combines molecular paleontology with experimental evolution, inserting ancient versions of genes into modern bacteria and observing how they evolve in response. I’ve puzzled over Uncommon Descent’s fondness for Dr. Kacar’s research before (“Evolution is evidence against evolution (?)“), and I’m afraid their new post on the topic (“Roll dice twice, see what turns up“) doesn’t really clear things up.

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Martian paleontology

NAISeminarsAt AbSciCon, I wrote about Mars Icebreaker, a proposed NASA mission that would search for signs of past and present life (“AbSciCon day 4: Mars, life, and Mars life“). Before Icebreaker, though, a new rover is scheduled to launch in 2020, with instruments designed to detect past and present biosignatures. Among these is the Planetary Instrument for X-Ray Lithochemistry (PIXL). On Monday at 1:00 PDT, Abigail Allwood from NASA Jet Propulsion Laboratory will be presenting a webcast seminar as part of the NAI Director’s Seminar Series:

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Volvox 2015: biophysics

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:

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Volvox 2015: evolution

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.).

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Excess of vigilance

Excess of vigilance

Fierce Roller gets a lot of spam comments, like several a day (I assume this is normal). If you are looking for cheap Ray-Ban glasses or NFL jerseys, I can hook you up. At some point in the last week or so I apparently hit “select all” before marking some new comments as spam, accidentally consigning all comments ever to spam purgatory. I have now restored all legitimate comments.

By the way, my (informal and subject to change) policy on comments is that I approve all of them unless they are straight up spam. I haven’t ever blocked a comment for any other reason.

Volvox 2015: development

Replica of Antonie van Leeuwenhoek's microscope.

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.

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Volvox 2015: me and my horsy and a quart of beer

Beastie-Boys-Licensed-To-Ill

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).

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Volvox 2015: cell differentiation

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

Erik Hanschen (left) with Cristian Solari, David Smith, and Jillian Walker

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