Alexey Desnitskiy from Saint Petersburg State University has published a new review of sexual development in the genus Volvox in the International Journal of Plant Reproductive Biology.
The article includes an up-to-date review of Professor Desnitskiy’s own work describing four developmental “programs” in the various species of Volvox:
The website for the Volvox 2017 conference is up at www.volvox2017.org. Registration isn’t open yet, but there’s some information about the venue, the Donald Danforth Plant Science Center in St. Louis. The meeting is set for August 16-19, 2017.
The goal of the International Volvox Conference is to bring together international scientists working with Volvox and its relatives (aka Volvocales or volvocine algae). We cordially invite experimentalists and theorists interested in these fascinating organisms.
I’ll keep you posted!
The following guest post was kindly provided by Dr. Kimberly Chen. I have edited only for formatting.
MicroRNAs (miRNAs) are a class of non-coding small RNAs that regulate numerous developmental processes in plants and animals and are generally associated with the evolution of multicellularity and cellular differentiation. They are processed from long hairpin precursors to mature forms and subsequently loaded into a multi-protein complex, of which the Argonaute (AGO) family protein is the core component. The small RNAs then guide the protein complex to recognize complementary mRNA transcripts and conduct post-transcriptional gene silencing.
Sex didn’t always involve males and females. I know it still isn’t always between males and females, but that’s not what I mean. I mean that there was a time when sex was happening, but there were no males and females. Sex existed before males and females, and many species are still doing it without them.
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).
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?
…”evolve” is not the correct term. The microbes adapted. – Cornelius Hunter
We heard several accusations during the recent Presidential campaign that one or the other candidate, or an interviewer, had taken a quote out of context. Of course, every quote is taken out of context. That’s what a quote is; otherwise it’s just the whole speech, or interview, or whatever. The important question is whether or not it’s taken out of context in a way that changes its meaning.
One thing I don’t do, and never have done, on this blog is intentionally misrepresent other people’s positions. The quote above, from a recent post by Cornelius Hunter on Evolution News and Views, means just what it says. He really is arguing that microbial adaptation observed in Lenski-style experiments is not evolution.
In response to “Behe’s bait and switch: on the falsifiability of intelligent design,” EnlightenmentLiberal comments:
I’ll take the stronger position that you can falsify intelligent design outright, and that is has been falsified, along with the rest of supernatural claims.
Michael Behe. Image from Uncommon Descent.
In a post on Evolution News and Views, Michael Behe sidesteps criticisms that intelligent design is not scientific with a bit of verbal judo. By conflating falsification of particular claims with falsification of intelligent design in general, he seems to back his critics into a rhetorical corner:
Now, one can’t have it both ways. One can’t say both that ID is unfalsifiable (or untestable) and that there is evidence against it. Either it is unfalsifiable and floats serenely beyond experimental reproach, or it can be criticized on the basis of our observations and is therefore testable. The fact that critical reviewers advance scientific arguments against ID (whether successfully or not) shows that intelligent design is indeed falsifiable.
Stephanie Höhn and Armin Hallmann have published a detailed study of the developmental process of inversion in Pleodorina californica. Pleodorina 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.
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]
One of the discussions I find most interesting in the philosophy of science is about what exactly constitutes a biological individual (or organism). The discussion would be a lot less interesting if everything were a vertebrate. Vertebrates (nearly always) develop from a single fertilized egg, so the (mostly) genetically homogeneous and (usually) genetically unique unit is the same as the spatially bounded, contiguous and physiologically integrated unit (this doesn’t even cover all the proposed criteria; see Clarke 2010 for a fairly comprehensive list with citations). But when we look outside of the vertebrates, what we often find is that some biological units have some of these properties and either groups or parts of those units have others.
Aphid on dandelion by Amoceann. Public domain image from Wikimedia Commons.