Heads I win; tails you lose: Evolution News & Views on Gonium, part 1


Figure 6 from Hanschen et al. 2016. Multicellularity hinges on the evolution of cell cycle regulation in a multicellular context with subsequent evolution of cellular differentiation (here, cell size-based) and increased body size.

Figure 6 from Hanschen et al. 2016. Multicellularity hinges on the evolution of cell cycle regulation in a multicellular context with subsequent evolution of cellular differentiation (here, cell size-based) and increased body size.

Remember how I said they’re prolific? Before I’ve even had a chance to write up my thoughts on the Gonium genome paperEvolution News & Views has already published theirs. The story has also been picked up by the Washington PostNew HistorianGenNews, and ScienceDaily (that last one looks like just a reprint of the press release from University of the Witwatersrand). By the way, the genome paper is open access, so you don’t need a subscription to see it for yourself.

We already know that cdesign proponentsists are not fans of research into the evolution of multicellularity, and that they have trouble understanding it. In an unsigned article on the Gonium genome at ENV, they admit that

After reading this paper, we’re none the wiser.

That’s too bad. I’m here to help.

They start by quoting from the ScienceDaily article press release, then describe the three volvocine algae with published genomes:

Gonium pectorale, a colonial algae [sic] where each cell is identical;

Chlamydomonas, a non-colonial algae [sic] (i.e., the cells don’t live together in colonies);

Volvox, another type of colonial algae that, however, does have differentiated cells.

Actually, Chlamydomonas cells do sometimes live together in colonies, but generally that’s right.

Of these three, only the last might arguably be considered a multicellular organism. Gonium pectorale is not a multicellular organism. Rather, each cell is an identical organism and they just live together in colonies.

Wrong and wrong. Gonium is, at least arguably, a multicellular organism, with a stable life cycle that consistently produces multicellular offspring, tight control of cell number (usually 8 or 16), and cytoplasmic bridges that connect the cells. Nor are the cells identical: the cells around the periphery have basal bodies that are rotated so that their flagella beat in parallel, rather than anti-parallel like those of the central cells (and of Chlamydomonas). If Gonium cells were disassociated, most of them would swim poorly. Cytoplasmic bridges and rotation of the basal bodies are best understood as adaptations at the colony level, indicating that Gonium is integrated, indivisible, and a unit of selection, all criteria for biological individuality.

The raw data is [sic] this: They sequenced the genome of Gonium pectorale and found that it has genes for cell regulation found in the non-colonial Chlamydomonas, but with a few differences. They put the Gonium pectorale versions of the genes back into Chlamydomonas and it grew into colonies. Not surprising.

O rly? It surprised the hell out of me when I learned about it at the last Volvox meeting.

Various authors at Evolution News & Views and Uncommon Descent have been arguing for years that the transition to multicellularity is really hard. Here’s Cornelius Hunter:

[The evolution of multicellularity] is yet another challenging topic because it contradicts the evolutionary model. The most obvious contradiction is that it requires a series profoundly sophisticated enhancements and changes to occur in a population of unicellular organisms.

and again:

Instead of the expectation that multicellularity arose once and then proliferated, evolutionists now must say it arose independently several times. And instead of a sort of primitive multicellularity emerging and then undergoing evolutionary refinement, we must believe evolution first produced profoundly unlikely molecular machines, which then in turn enabled multicellularity.

Ann Gauger on Volvox (I addressed her assertions here and here):

Missing from this story, though, are the details necessary for this 12-step progression to occur. There’s the matter of incomplete cell division, cell separation later, and matrix formation. Then there’s the matter of specialization. To get the specialization of somatic from germ cells requires the development of at least three proteins. Also, the embryos produced by those reproductive cells are inside out — the flagella are on the inside, which makes them useless for swimming, and the gonidia are on the outside. As a result, the embryo must turn itself inside out when it reaches the right size. This requires that the somatic cells change shape to bottle- or spindle-shaped cells, depending on their position in the embryo. This shape change requires both microtubules and a little motor protein called kinesin. Neither microtubules or kinesin are present in bacteria so their origin must be accounted for. The selective advantage of each step is not clear.

A very nice example of Intelligent design’s double standard: we need to know the exact mechanisms and selective advantages of every step for an evolutionary explanation to even be plausible, while intelligent design argues away the need to even propose a mechanism.

Michael Behe commented on Will Ratcliff’s yeast multicellularity experiments:

The authors did not analyze the genetic changes that occurred in the cells, but I strongly suspect that if and when they do, they’ll discover that functioning genes or regulatory regions were broken or degraded. This would be just one more example of evolution by loss of pre-existing systems, at which we already knew that Darwinian processes excel. The apparently insurmountable problem for Darwinism is to build new systems.

But in response to the Gonium genome paper, the simple genetic basis of multicellularity is “Not surprising.” In fact,

…apparently early stages of this evolution gave exactly what you needed (the “template” was “laid out”) for multicellularity. Isn’t that lucky! It sounds like front-loaded intelligent design.

So let me get this straight: if multicellularity is really complicated, that’s evidence for intelligent design. But if multicellularity is really simple, that’s evidence for intelligent design. Heads I win; tails you lose!

I really hadn’t intended to make this a two parter, but I have a lot to get done before the weekend, and I still have to write part 3 on O’Malley and Powell’s critique of major transitions theory, not to mention an actual substantive post on the Gonium genome. There is a lot more wrong in the ENV post, and let’s face it, creationists talking about multicellularity is pretty much my sweet spot, so stay tuned.

 

Stable links:

Hanschen ER, Marriage TN, Ferris PJ et al. (2016) The Gonium pectorale genome demostrates co-option of cell cycle regulation during the evolution of multicellularity. Nature Communications, 7, 11370.

Kirk DL (2005) A twelve-step program for evolving multicellularity and a division of labor. BioEssays, 27, 299–310.

Lurling M, Beekman W (2006) Palmelloids formation in Chlamydomonas reinhardtii: defence against rotifer predators? Annales de Limnologie, 42, 65–72.

 

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