Invasive Pleodorina indica in Poland

Figure 3 B-I from Knysak and Żelazna-Wieczorek 2017. Pleodorina indica (Iyengar) H. Nozaki 400x.

Figure 3 B-I from Knysak and Żelazna-Wieczorek 2017. Pleodorina indica (Iyengar) H. Nozaki 400x.

A new paper in Oceanological and Hydrobiological Studies reports a massive bloom of Pleodorina indica in a reservoir in central Poland. Piotr Knysak and Joanna Żelazna-Wieczorek sampled the reservoir on the Olechówka River in Łódź during the summer of 2015 and found that P. indica made up ~95% of the algae collected.

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Pandorina(?) in The Atlantic

In The Atlantic, not in the Atlantic. A new article in The Atlantic is making the rounds on social media, “Scientists Brace for a Lost Generation in American Research.” The article speculates on the likely long-term effects of President Trump’s proposed ~20% cut to the NIH budget. Which is fine, because what has the NIH ever done for us? Okay, there was the whole genetic code thing, plus

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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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What is a (Volvox) species?

Hisayoshi Nozaki and colleagues have just described some Volvox samples from two lakes and a pond in Japan.

Figure 1A from Nozaki et al. 2016. Volvox sp. Sagami asexual spheroid with daughter colonies (d).

Figure 1A from Nozaki et al. 2016. Volvox sp. Sagami asexual spheroid with daughter colonies (d).

The newly collected strains have a lot in common with another recently described species, Volvox ferrisii, but there are some important differences as well:

…it could be clearly distinguished from all previously described monoecious species of Volvox sect. Volvox by its small number of eggs or zygotes (5–25) in sexual spheroids, with short acute spines (up to 3 μm long) on the zygote walls and elongated anterior somatic cells in asexual spheroids.

In spite of these differences, Nozaki and colleagues stop short of calling the newly collected strains a new species. Why?

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Initiation of cell division in Chlamydomonas

Deborah Shelton and colleagues have published a new article arguing that the reigning model of cell division initiation in Chlamydomonas reinhardtii needs to be revised [full disclosure: Dr. Shelton and I were labmates in Rick Michod’s lab at the University of Arizona]. The evolution of multicellularity almost certainly involved changes in cell cycle regulation; for example, there is good evidence that changes to the cell cycle regulator retinoblastoma were involved in the initial transition to multicellular life in the volvocine algae. So understanding cell cycle regulation is vital for understanding the evolution of multicellularity.

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Spheroids without inversion: Astrephomene development

Algae in the family Volvocaceae are (with one exception) little spheroids that swim around in freshwater lakes, ponds, and puddles. Volvox is by far the most famous of these algae, but there are a number of smaller genera, including Eudorina, Pleodorina, and Pandorina:

Fig. 1 from Herron 2016. Examples of volvocine species. (A) Chlamydomonas reinhardtii, (B) Gonium pectorale, (C) Astrephomene gubernaculiferum, (D) Pan- dorina 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. Figure Credit for A and B: Deborah Shelton.

Fig. 1 from Herron 2016. Examples of volvocine species; D-O are in the family Volvocaceae. (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. Figure Credit for A and B: Deborah Shelton.

All of the members of this family have a problem: at the end of cell division, they find themselves in an awkward configuration, with their flagella on the inside. Each cell has two flagella, and the algae need them on the outside to be able to swim. They achieve this through a developmental process called inversion, essentially turning themselves completely inside-out during embryogenesis. Even the one member of the family that is not spheroidal, Platydorina (F in the figure above), undergoes inversion before flattening into a horseshoe shape. The ways in which they do this are complex and diverse (see for example “Pleodorina inversion” and “The most important time of your life“), but not the topic of this post.

The sister group to the Volvocaceae, the Goniaceae, also includes a spheroidal genus, Astrephomene (C in the figure above). Although Astrephomene looks a lot like some of the Volvocaceae, say Eudorina (I) or Pleodorina (J), it doesn’t undergo inversion!

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Pleodorina inversion

Stephanie Höhn and Armin Hallmann have published a detailed study of the developmental process of inversion in Pleodorina californicaPleodorina is one of the two genera we usually refer to as ‘partially differentiated’ (the other is Astrephomene), meaning that some of their cells are specialized for motility and never reproduce (soma) and some perform both motility and reproductive functions. P. californica is pretty big, up to about 1/3 of a millimeter, easily visible to the naked eye (though you’d need better vision than mine to make out any details).

Stephanie Höhn sampling a pond near Cambridge University during the Volvox 2015 meeting.

Stephanie Höhn sampling a pond near Cambridge University during the Volvox 2015 meeting.

Like all members of the family Volvocaceae, P. californica undergoes complete inversion during development:

After the completion of the cell division phase and before inversion, the embryos of Gonium, Pandorina, Eudorina and Pleodorina consist of a bowl-shaped cell sheet, whereas the embryonic cells of Volvox form a spherical cell sheet. With exception of the genus Astrephomene, all multicellular volvocine embryos face the same “problem”: the flagellar ends of all the cells point toward the interior of the bowl-shaped or spherical cell sheet rather than to the exterior, where they need to be later to function during locomotion. [References removed]

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Volvox 2017 – save the date

The Fourth International Volvox Conference will be held in St. Louis, Missouri August 16-19, 2017, with Jim Umen organizing.

Starting in 2011, we have had a Volvox meeting every other year (every year there’s not a Chlamydomonas meeting, that is). The first meeting was at Biosphere 2 outside of Tucson, Arizona, the second at the University of New Brunswick, and the third at Cambridge University.

Biosphere 2

Biosphere 2, the site of the First International Volvox Meeting in 2011.

You don’t have to study Volvox to join us; the meeting is open to anyone with an interest in the evolution of multicellularity (last year’s invited speaker was Professor Pauline Schapp, who studies cellular slime molds).

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