Mutation, selection and complexity

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A while ago on ASA, Glenn Morton referenced the work by Boraas. I have always been fascinated by this reference but unable to find much relevant literature. Until recently, when I accidentally ran across more recent reearch in this area. I would like to share what I learned and how these findings may help understand evolution of multicellularity.

The original references was to a paper published in EOS called “Predator-mediated algal evolution in Chemostat culture”. In 1998, Boraas published another paper titled “Phagotrophy by a flagellate selects for colonial prey: A possible origin of multicellularity” in Evolutionary Ecology 1998, 12, 153-164

According to the original abstract, an unknown predator had invaded a chemostat containing algae. While many of the algae fell prey to the predator, a news species arose consisting of clusters of multiple cells. This seems the first logical step towards full multi-cellularity where cells take on specific roles.

The original abstract reads

An unidentified microflagellate specie (4-12 [mico]m) and Chlorella Prenodosa (2-5 [micro]m) were grown at 25 C in mixed-species chemostats with constant light and sterile, inorganic medium flow. The flagellate readily consumed the algae and grew rapidly (doubling time ca. 6 h). Size distributions of both species are shown in the Figure (area = biovolume). After an initial oscillation (curves 1,2), the system apparently stabilized with both species coexisting. The algal population now consisted of clusters of 4 to tens of cells that were immune to predation by the flagellate (curve 3). The mean cluster size then steadily decreased (curve 4) and stabilized at 4-8 cells (curve 5). These, and other, observations support the hypothesis: (1) a multicellular algal form was selected as a response to predation pressures, (2) a minimum cluster size was selected due to nutrient competition (large clusters have a smaller surface area per unite biomass) and (3) genetic, morphological, and structural diversity of the system increased as a response to predation. Flagellate predation influences both the genetics and the dynamics of microalgal population.”

the 1998 paper reports on experiments with predation

Summary

Predation was a powerful selective force promoting increased morphological complexity in a unicellular prey held in constant environmental conditions. The green alga, Chlorella vulgaris, is a well-studied eukaryote, which has retained its normal unicellular form in cultures in our laboratories for thousands of generations. For the experiments reported here, steady-state unicellular C. vulgaris continuous cultures were inoculated with the predator Ochromonas vallescia, a phagotrophic flagellated protist (‘flagellate’). Within less than 100 generations of the prey, a multicellular Chlorella growth form became dominant in the culture (subsequently repeated in other cultures). The prey Chlorella first formed globose clusters of tens to hundreds of cells. After about 10-20 generations in the presence of the phagotroph, eight-celled colonies predominated. These colonies retained the eight-celled form indefinitely in continuous culture and when plated onto agar. These self-replicating, stable colonies were virtually immune to predation by the flagellate, but small enough that each Chlorella cell was exposed directly to the nutrient medium.

The article showed how when a common uni-celllular alga “Chlorella vulgaris” was exposed to a predator “Ochromonas vellesiaca”, a phagotrophic flagellate, within 100 generations or so, a multicellular (colonial) specie arose .

The results were discussed in a 2000 TalkOrigins Post of the Month by Adam Noel Harris and in TalkOrigin’s Index to Creationist Claims CB904

In other words, the innovsative step from single to multi-cellular may well have taken place under selective pressures of predation. The work by Boraas shows that even accidents such as allowing predators iside chemostats can lead through hard work to fascinating new scientific findings and insights.

The authors mention that other than in rare instances, the Chlorella culture had always exhibitied its normal unicellular morphology over a timeframe of 2 decades.

When the predator was introduced, predictably the prey density declined and the predator density increased. When the predators started to run out of food, they started to decline and the reduction in predation led to a recovery of the Chlorella population (this is a classical pre-predator interaction). During the recovery phase, it was noticed that in addition to unicellular forms, there now existed colonial forms with the numbers of cells ranging from four to hundreds. Eventually the system entered a steady state with the Chlorella population consisting of colonies of 8 cells. These colonies were not only stable but also self-replicating

The authors conclude that the muli-cellular form is a rare mutation which was selected by predation and thus ‘amplified’. The authors also discuss the issue of induction, namely that the flagellates released a substance that caused colony formation. Given that it took almost 20 generations before colonies became apparant, the authors reject this alternative. Additionally, multicellular colonies were maintained even in low density cultures and finally, when the colonies are allowed to reproduce by themselves, they reproduce as colonies not single cells. The authors finally show how these experiments support a thesis by Stanley that multicellular life arose late into the pre-Cambrian under selective pressure of predation. Was the Cambrian explosion in other words, an arms race between prey and predator?

That under selective pressure, mulicellular colonies arose, shows how the simple processes of variation and selection can surely explain innovation and increase in complexity.

Stanley, S.M. (1973) An ecological theory for the sudden origin of multicellular life in the Late Precambrian PNAS 70, 1486-1489.

According to modern ecological theory, high diversity at any trophic level of a community is possible only under the influence of cropping. Until herbivores evolved, single-celled algae of the Precambrian were resource-limited, and a small number of species saturated aquatic environments. In the near-absence of vacant niches, life diversified slowly. Because the changes required to produce the first algae-eating heterotrophs were therefore delayed, the entire system was self-limiting. When the “heterotroph barrier” was finally crossed in the late Precambrian, herbivorous and carnivorous protists arose almost simultaneously, for no major biological differences separate the two groups. These events automatically triggered the formation of a series of self-propagating feedback systems of diversification between adjacent trophic levels. Comparable systems arose among multicellular groups, which radiated rapidly from the newly diversifying protist taxa. The sudden proliferation of complex food webs formed by taxa invading previously vacant adaptive zones produced an explosive diversification of life over a period of a few tens of millions of years. The rapid appearance of skeletons in various groups, though of special geological importance, was no more dramatic than other aspects of the radiation. The overall rate of diversification was comparable to rates for less-extensive adaptive radiations of the Phanerozoic.

256 Comments

Re “Was the Cambrian explosion in other words, an arms race between prey and predator?”

Fascinating!

Great post and great topic!

Question - anyone know any good research on why multicellular organisms are almost all eukaryotic?

Another green Algae also provide a nice example as to how sex may have evolved (Andy/Larry? are you listening?) From this link we learn that chlamydomonas divides both sexually and asexually. Sexual reproduction is stimulated by environmental stress.

Many features of chlamydomonas sex are believed to have evolved early in the chlorophyte lineage. Using this basic life cycle, many refinements that evolved among the chlorophytes have been identified.

  • Some green algae produce gametes that differ from vegetative cells, and in some species, the male gamete differs in size or morphology from the female gamete (anisogamy)
  • Many species exhibit oogamy, a type of anosogamy in which a flagellated sperm fertilizes a nonmotile egg.
  • Some multicellular species also exhibit alternation of generations
  • Ulva produces isomorphic thalli for its diploid sporophyte and haploid gametophyte.

From isogamy where both “egg” and “sperm” are one and the same, to anisogamy where the egg hecomes the larger and the sperm the smaller one to oogamy where the sperm is now flagellated and fertilizes an egg with no flagella.

Cool stuff

Using these relatively simple organisms, we can ‘re-create’ plausible pathways for the evolution of multi-cellularity, the evolution of sex and the evolution of diversification. Not bad

This would appear to be analogous to recent events at Uncommonly Decent. The Blog has become multi-cellular but in addition displays cellular specializations. The appointment of a Blog Czar with online banning and censorship powers indicates an additional level of complexity and cellular specialization. While PT is also characterized by multiple contributors and can be considered multi-cellular the cellular specialization found at UD is lacking and suggests that predation (selection) is much stronger on that population and recent events such as the Kitzmiller decision support that conclusion. The resultant population stability observed in newly evolved multi-cellular Chlorella algae suggests that ID and belief based notions about biological complexity will continue to survive. Since it is hypothesized that minimum cluster size is dependent upon nutrient access, the best method to combat large clusters is better science education reducing available nutrients.

Delta Pi Gamma (Scientia et Fermentum)

It seems quite obvious that there was simply an environmental response on the part of Chlorella when in the presence of a predator. It’s much harder to “eat” a multicellular globule. It’s quite obvious that the “machinery” for responding is “built-in”. This isn’t evolution in the least.

This highlights the difference between ID and neo-Darwinism: experiments like this are completely misunderstood.

This highlights the difference between ID and neo-Darwinism: experiments like this are completely misunderstood

lol. that’s just perfect, blasty.

couldn’t have said it better myself. Now if you could only realize the truth of what you said is the exact opposite of the meaning you intended.

*sigh*

Blast Wrote:

It seems quite obvious that there was simply an environmental response on the part of Chlorella when in the presence of a predator. It’s much harder to “eat” a multicellular globule. It’s quite obvious that the “machinery” for responding is “built-in”. This isn’t evolution in the least.

This highlights the difference between ID and neo-Darwinism: experiments like this are completely misunderstood.

ROTFL, but no it was not an induced response and the researcher tested against such scenario but rather more likely a rare mutation being selected for. There are many good reasons why your ‘explanation’ fails. If it were a built in response, why did it take 100 generations and many dead ‘algae’ before slowly multicellular forms arose?

Under non-predation circumstances, the cost of colonization may be too high but add in another factor and voila speciation, and not just any speciation but an important step from single to multicellular.

So why is it not evolution: 1. Variation 2. Selection 3. Speciation

As to your ‘explanation’ could you be more specific as to the details? What machinery, when was it ‘built in’? You know, them pesky, what did Dembski again call them? oh yes, pathetic details.

Given the response, is there anyone left who denies that ID is scientifically vacuous?

Sir Toejam, that’s funny, had not noticed the Freudian slip here. Why is it so hard for ID activists to accept evolutionary theory? I thought that ID embraced evolutionary theory? After all, that’s why it presents no real scientific explanations of its own relevant to its thesis.

If Blast is interested in examples of induced response, then there are good papers out there

Hessen and Van Donk (1993) discovered the involvement of a chemical cue released from the zooplankton in stimulation of colonies. The addition of filtered medium from a Daphnia culture to unicellular Desmodesmus subspicatus populations resulted within two days in populations dominated by colonies, while the controls remained unicellular.

as to why it is apparently so hard to get IDers to recognize the science involved in evolutionary theory, and the tremendous evidence in support, I came to the conclusion long ago that most are suffering from a common psychological disorder.

go take a look at a freshman psych text that goes into standard freudian defense mechanisms sometime.

the physchological pressure these folks feel between their constructed belief systems and the reality of the world as it presents itself to them motivates them subsconsciously to produce ever more extreme and bizarre forms of defense mechanisms.

typically, these seem to take the form of projections, as blast has just so wonderfully demonstrated for us just now, and frequently has in the past.

Denial is also a very common defense mechanism among many ID supporters.

I swear, someone could easily write a series of papers extolling the remaining virtue in freudian psychology simply by using creationists as a research group.

As I explained Boraas et al also discussed the induction alternative and rejected it based on the following reasons

Our results could be interpreted as evidence that the flagellates released a substance inducing colony formation in Chlorella, similar to predator-induced morphological changes in zooplankton (Dodson, 1989) and in coccoid green algae (Hesssen and van Donk, 1993). We discount this alternative hypothesis, based on four observations. First, colonies did not become apparent for about 20 Chlorella generations after inoculation of the flagellates. An ‘induction’ should have been expressed as soon as the inducing substance produced by the flagellates had reached some critical concentration. Secondly, once it has appeared, the colonial growth form has been maintained in mixed-species cultures for over 2 years, even at low flagellate densities. Induction should vary with flagellate density. Thirdly, when the colonies are cultured in the absence of any source of an inducing substance, the colonies ‘breed true’. The colonial Chlorella morph remains colonial both on agar and in monospecific liquid culture, including chemostats where steady states have beenmaintained for several months. Finally, in nitrogen-limited, two-stage chemostats where both stages are illuminated, with unispecific Chlorella in the ®rst stage and mixed Chlorella-Ochromonas in the second stage, we see colonial Chlorella. These Chlorella must be growing on the inorganic nitrogen excreted by Ochromonas. When the second stage is darkened, the Chlorella colonies rapidly wash out of the culture, leaving only the unicellular Chlorella supplied from the first stage and, of course, their flagellate predators. This shows that active photosynthesis by the algae and continued interaction with the predator are essential to maintain the colonial algae in continuous culture. When cultured in the absence of the predator, the cell size of the unicells in the second stage declines, showing that cell division and associated morphogenetic processes are taking place, but the colonies are not formed in the absence of the predator.

Hope this helps. Don’t worry, there is far more fascinating stuff. Multicellularity, evolution of sex… Cool stuff.

Wikipedia has some interesting stuff on cognitive dissonance see also here

Our minds work in mysterious ways and such little time to learn about all this cool stuff.

yes, I’ve heard the conflict between some religious worldviews and objective reality described as a form of congnitive dissonance before; more specifically, the wiki article you mentioned best describes this as follows:

The more well-known form of dissonance, however, is post-decisional dissonance. Many studies have shown that people with compulsive disorders like gambling will subjectively reinforce decisions or commitments they have already made. In one simple experiment, experimenters found that bettors at a horse track believed bets were more likely to succeed immediately after being placed. According to the hypothesis, the possibility of being wrong is dissonance-arousing, so people will change their perceptions to make their decisions seem better.

it sounds ludicrous to those who aren’t suffering from this that someone would actually “change their perceptions to make their decisions seem better”, but it’s been documented so many times as to be considered commonplace.

now, I’m not saying that all of ID exists solely becuase of some psychological schism. Indeed, there is a lot of evidence to indicate that the specifics of the strategy may have been designed as more political strategy (not for ideology’s sake, but merely to better control and maintain a significant grassroots power base) than as a result of ideological postulates.

However, from what I have seen of many creationists (blast being a great example), the tenants of ID seem almost tailor-made to act as a lure for those suffering from the type of dissonance I am speaking of here, just as “creation science” was 40 years ago.

this would also explain why a large proportion of xians in the US (and around the world) are NOT attracted to ID. they simply aren’t suffering this type of dissonance.

Along with politicians, who are using ID in order to maintain their right-wing political base (think Santorum and GW as good public examples), the other “pushers” taking advantage of this are those doing it to make money, like Dembski. This explains why folks like Dembski, who are obviously more intelligent than they “play on TV”, keep repeating the same drivel over and over again, even though they themselves admit to the inadequacy of ID as science, or even theory. They know they have a “captive audience”, desperate to have someone throw out something to alleviate their dissonance; something they can easily “change their perceptions” to fit their worldview.

It’s very much like a pusher selling crack to the addicted.

It’s not the motivations of folks subject to a psychological disorder, like blast, that disgust me. It’s the pushers like Dembski, and the “casino owners” like GW.

True conservative republicans have been deriding the reliance on this powerbase for decades now.

However, instead of a decreasing placation and manipulation of this group, the current neocons, led by Karl Rove, instead seem to be expanding their abuse of these folks in order to gain ever more power and control.

It sickens me to no end.

PvM Wrote:

ROTFL, but no it was not an induced response and the researcher tested against such scenario but rather more likely a rare mutation being selected for. There are many good reasons why your ‘explanation’ fails. If it were a built in response, why did it take 100 generations and many dead ‘algae’ before slowly multicellular forms arose?

You say that it’s “more likely a rare mutation”. So you don’t know. You’re guessing.

Now, if it’s a “rare mutation”, a “rare mutation” in what? ONE of the chlorella? Or is it a case of “simultaneous rare mutations” in a number of the chlorella? Multicellularity is a kind of “social” behavior on the part of the chlorella, so perhaps that’s why it takes time (100 generations) to bring about. It’s entirely possible that the chlorella start producing some kind of protein in the presence of predators which, when reaching a certain critical concentration, triggers the multicellularity response.

You say it’s not an “induced” response. But, of course, it is one way or the other: viz., whether it is ‘induced’ by the ‘predator’ or induced by some other chemical/protein, it’s an ‘induced’ response.

And how did the experimenter test that this wasn’t the case? It would have been nice to have included that information.

You say that it’s “more likely a rare mutation”. So you don’t know. You’re guessing.

Now, if it’s a “rare mutation”, a “rare mutation” in what? ONE of the chlorella? Or is it a case of “simultaneous rare mutations” in a number of the chlorella?

Multicellularity is a kind of “social” behavior on the part of the chlorella, so perhaps that’s why it takes time (100 generations) to bring about. It’s entirely possible that the chlorella start producing some kind of protein in the presence of predators which, when reaching a certain critical concentration, triggers the multicellularity response.

You say it’s not an “induced” response. But, of course, it is one way or the other: viz., whether it is ‘induced’ by the ‘predator’ or induced by some other chemical/protein, it’s an ‘induced’ response.

And how did the experimenter test that this wasn’t the case? It would have been nice to have included that information.

Allow me to address some of this in pieces:

1) “Most likely” is not referring to an uneducated guess here. This is an educated conjecture based on data that is sufficient to establish a degree of certainty, but not 100% truth in all situations bar none no matter what. He’s not just “guessing”. You misconstrue the wording, and I think it’s probably deliberate, as the other option is that you’re quite plainly not very bright.

2) Mutations occur in DNA sequences. I’m not really sure what your question is, but it appears nonsensical to me. I have not read the study, obviously, but the implication seems to be that a mutation occurred in a single-celled organism which encouraged it to either itself become multi-cellular OR allowed it to, in some way, gather other single-celled organisms into a larger whole. I’d have to research it to give you a good answer… but you could answer your question yourself by researching it. Again, I think it is willful ignorance that prevents this. If you legitimately don’t know how to research, I’m sure if you ask politely we’d be happy to share.

3) As to your third paragraph - I see a 20 generation timeframe for the initial multi-cells to erupt onto the scene, and then over time (should they have an advantage in reproduction thanks to survivability, which they did) they would gradually become the dominant force. This is what occurred. Precisely what is your question getting at? As to the “producing a protein” part, again, read the summary alone. They address that, and if that was true, you would not need the many generations that passed in order to undergo a change. I’m also pretty sure you could control and/or test for it. If you think that’s the correct theory, I suggest you actually test it! They have produced results - if you dispute them, you must do the work to disprove them yourself. The burden of proof is now on you.

4) You are not using the same definition of induced as the author of this summary, and that is where your confusion comes from here. In their case, “induced” is not meant to include the natural environmental pressure from the predators. In your case, it is. Sort that out and you see the problem. Again, I think you are doing this willfully, or are you incapable of basic reading comprehension?

So, in closing, I see some problems. You change contexts wildly and then try to argue the original arguments based on an entirely different context. You are using different definitions from the authors, but attempt to superimpose your definitions on theirs and thus alter the message they were conveying improperly. Lastly, you display (willful?) ignorance of the scientific process in very basic and fundamental ways. I suggest you learn how to rectify these issues in the future, lest you be taken even less seriously than you currently are. I’m not saying this to be a jerk, either - I fully welcome informed debate by all sides.

I tire, however, of wildly uninformed “debate” (and I use that word only in the most sarcastic sense possible).

Test it yourself! That’s too much. I’m sorry.

And btw, of course, I think ID is a waste of time and can explain nothing, but please…

Multicellularity is a kind of “social” behavior on the part of the chlorella, so perhaps that’s why it takes time (100 generations) to bring about. It’s entirely possible that the chlorella start producing some kind of protein in the presence of predators which, when reaching a certain critical concentration, triggers the multicellularity response.

changing perceptions to fit worldview.

check.

It’s not even CLOSE to being in the same category as any kind of correctly defined social behavior Blast.

Can’t you see how you are twisting your own perceptions?

hell, you’re going so far as to try to put square pegs into round holes even!

AD Wrote:

I’m not saying this to be a jerk, either - I fully welcome informed debate by all sides.

That’s quite nice of you. May I point out a few things:

(1) When it came to responding to what I said was no more than a ‘guess’, you respond that it is an “educated guess”. How very informative! (2) When I ask if the ‘mutation’ is in ONE of the chlorella or more than one you respond by saying “the implication seems to be that a mutation occurred in a single-celled organism which encouraged it to either itself become multi-cellular OR allowed it to, in some way, gather other single-celled organisms into a larger whole. I’d have to research it to give you a good answer.” You’re guessing. Is that “informed debate”? (3) Regarding the ‘multicellularity’ you seem to suggest that they covered that (And I presumed that they TRIED to cover that.). But without knowing further details, it’s hard to know. You yourself write: “They address that, and if that was true, you would not need the many generations that passed in order to undergo a change. If that were true? Is this informed debate too? (4)As to “inducing”, you write: You are not using the same definition of induced as the author of this summary, and that is where your confusion comes from here. In their case, “induced” is not meant to include the natural environmental pressure from the predators. Why do you assume I’m “confused”? You write that “in their case ‘induced’ is not meant to include the natural environmental pressure from the predators. Thank you for pointing out the obvious. The point is that ‘induced’ has a generalized meaning; and within that generalized meaning, the presence of the predator brings about a response (induced) in Chlorella. Did you notice my last comment where I said that it would have been nice for them to have included this information. Again, let’s hear it for “informed debate”. I’m waiting for the information.

Sir Toe Jam Wrote:

hell, you’re going so far as to try to put square pegs into round holes even!

Yeah, and when you put quotation marks around a word, it’s possible to fit square pegs into round holes. Or are you not paying attention?

putting quotes around a word does not totally change its meaning, except maybe in your own mind there, blasty.

it implies the word generally fits the category of usage, with exceptions.

however, in the way you use it, you might as well have used the word “metallic”.

you selective use of quotes around words only serves to indicate the spots where you are selectively applying your very own constructed perceptions.

hence that’s why i made a point of it.

you exhibit this behavior commonly. perhaps without even realizing it. You ARE suffering from a form of dissonance.

As to whether that’s curable or not, you’d have to visit a mental health professional.

no shame in that; mental illness is just like any other physical ailment.

I wish you luck.

Blasty,

Let’s try this again, but if you continue to use the same disingenuous tactics, I’m going to cease bothering:

1) You disparagingly called something a guess, with the implication being that it was obviously unfounded. An educated guess (also known as a professional estimation) is something that is well-founded but accepts a small degree of potential uncertainty. These are not the same thing. For instance, you would be guessing what color my dog is, but I could make an educated guess about the potential standard deviation on a specific set of data, given that I’m a mathematician.

2) A mutation, by definition, is contained within one strand of DNA. This is why your question is nonsensical. Concurrent identical mutation across multiple organisms is something that is not predicted (unless there is some method of directly transferring DNA between non-offspring relational organisms) by evolution, thus IF that is what you were asking, your question is just plain stupid. It should be obvious that’s not the case, if you had done the background research. My “guess”, which is in this case an “educated guess”, as above, is predicated around that fact which you were apparently not in possession of. Also, you might notice I advised you to verify, which you shockingly failed to do. I made an educated guess and informed you how to check it, yet you both failed to understand that and then failed to check it.

3) You’re cherry picking my quotes here. Let’s back up and add that magical thing known as context. First, there are statements about your comment on the cause of multi-cell colonies in the summary of the article. So let me ask you: did you not read it, or did you not understand what you read? We’re out of other options, because you just claimed they didn’t address it. Which one was it? Secondly, when I said “IF that were true” I was alluding to your previous statement, with the implication being that it was not, in fact, true. In the same way I now say that if you were capable of even a basic level of reading comprehension, we wouldn’t be having this discussion, because you’d already have realized your questions were answered. However, that’s obviously not the case. I assumed (foolishly) that you were not so stone cold stupid as to be incapable of picking up on very basic and commonly used implication in the english language. I was quite clearly wrong.

4)

Thank you for pointing out the obvious. The point is that ‘induced’ has a generalized meaning; and within that generalized meaning, the presence of the predator brings about a response (induced) in Chlorella.

Except that they weren’t using the generalized meaning! This is precisely the problem you are having. I can certainly claim that “engine” has a generalized meaning that might refer to say, a steam or coal engine, but it’s understood that when an auto mechanic speaks about a car engine, he’s referring to an internal combustion engine. Well, that is, unless you’re too dense to pick up on context, which again appears to be the case here. They weren’t using the generalized meaning. If you try to apply a generalized meaning to their argument in response, you’re just plain wrong.

Thus, if you’re going to post again, I suggest that you either become literate in a most basic fashion and learn how to fact-check, or that you actually stop being a lying, disingenuous snake, depending on which is the case. Also, I notice you still have not offered to perform any experiments or back up your conclusions, when the burden of proof is upon you. You fail on multiple levels here, and I think that should be apparent to the general audience reading this thread. Should you continue to replicate these failures (or introduce similarly obvious ones), I’ll stop wasting time on you.

Better luck with your next post.

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Sir Toe Jam Wrote:

As to whether that’s curable or not, you’d have to visit a mental health professional.

no shame in that; mental illness is just like any other physical ailment.

So, it seems that the high priests of Darwinism have moved beyond the Inquistion and “witch trials”, and are now employing that tactics of Stalinist Russia to stamp out dissent. “He doesn’t believe in Communism. He must be mentally ill.”

Tell me: are you guys religious fanatics, communist dictators, or just plain fascists? I’m curious to know.

Ah, the sound of denial… A first step towards recovery from cognitive dissonance

Blast Wrote:

They say that in order for the “colonies” to persist, the predator has to be present. And when the predator is taken away then the colonies go away. Is there not enough room in the word “induction” to cover such a situation? The only reason that they don’t use “induction” is because it took 20 generations to bring about an initial change. To them that’s “proof” that “induction” didn’t take place. Again, where’s the rule that says that “induction” has to take place quickly?

Nope, they gave four reasons. Have you not been following the discussion? Or have you not read the paper (eeks!!!)

There is nothing miraculous about this experiment. The algae have a rare variant which is multicellular. When under environmental pressure, such variants are ‘amplified’ leading to colonies of 4 to hundreds of cells, finally reaching a steady state of 8.

Thirdly, when the colonies are cultured in the absence of any source of an inducing substance, the colonies ‘breed true’.

Why so much opposition to what science has found? If Blast disagrees, he can present his own research and experiments to support his claims. But induction was considered and rejected on good grounds.

And it either way the response is induced then why are we arguing? You seem to be suggesting that your induction idea is similar to the selection argument?

PvM: You’re always even-headed and open-minded. Good for you.

You wrote, in relation to the possibility of “induction”: “Nope, they gave four reasons. Have you not been following the discussion?”

Well, here’s the problem:

Thirdly, when the colonies are cultured in the absence of any source of an inducing substance, the colonies ‘breed true’. The colonial Chlorella morph remains colonial both on agar and in monospecific liquid culture, including chemostats where steady states have beenmaintained for several months. … (later on)This shows that active photosynthesis by the algae and continued interaction with the predator are essential to maintain the colonial algae in continuous culture.

This doesn’t seem to rule out the possibility of the predator flagellate being the “inducer”: meaning that it interacts with chlorella, either directly or indirectly, bringing about a pre-packaged response in the Chlorella.

Is there some technical detail I’m missing here?

Bile does not substitue for erudition. So try a different tact, please.

Erudite us, Blast. Explain to us how “frontloading” works.

(sound of crickets chirping)

Yep, that’s what I thought. All mouth.

Read Michael Denton’s criticism in “Evolution: A Theory in Crisis”. Hope that helps.

Then read (1) Denton’s next book, which explains why his previous book was wrong, and (2) Denton’s request to be removed from the DI’s list of Fellows and supporters.

Hope that helps.

I’d like to hear Blast explain why Darwin was wrong about varieties and incipient species? And why should we rely on Denton whose book seems in many aspects to be quite flawed.

I’ve allowed myself, let us say, a ‘cooling off period.’

I’m very disillusioned with the attitude of the people on this board—and that includes you, Pim.

You all seem to lack any ability whatsoever to admit that there might be problems should those problems tend to undermine, in any way at all, the hallowed Darwinian orthodoxy.

PvM Wrote:

Hmm, I assumed you had read the paper “The cells in these stable colonies of predated cultures were enclosed within an envelope (Fig. 1d), apparently the mother cell wall of the neonatal cells (see Discussion). Empty mother cell walls were virtually absent from the culture.”

Yes, I’ve read the paper more than once. And I also read, “The most probable initial mechanism for colony formation, adhesion of the daughter cells to the mother cell wall, is suggested by two observations: the membrane that surrounds the colonies (Fig. 1d) and the absence of cast-off mother cell walls in cultures dominated by colonial morphs (personal observation).” So, which is it? Are they ‘virtually absent’, or are they ‘absent’, period? Wouldn’t it be nice to know?

This points out a serious problem with this paper: inconsistency in reporting and terminology. Where were the peer-reviewers?

As I say, it’s a serious problem.

We’ve already gone round and round on this: but what, exactly, constitutes a “multicell”? On one page of their paper they call it a ‘colony’, then it’s a ‘multicell colony’, and then they talk flat out about ‘multicells’. Why can’t they get their terminology consistent? Again, where are the peer-reviewers?

They’re also inconsistent in their reasoning.

For example, what is their reason for ‘discounting’ chemical induction? The principal reason given is that: “First, colonies did not become apparent for about 20 Chlorella generations after inoculation of the flagellates. An ‘induction’ should have been expressed as soon as the inducing substance produced by the flagellates had reached some critical concentration.” (p. 159) Yet, on the SAME PAGE, they write: “In a system where environmental conditions were held constant, a multicellular organic form evolved from a unicellular one within 10±20 generations.” Well, again, which IS IT: 10 or 20 generations? When it comes to their MAIN reason for discounting chemical induction, they equivocate! Amazing!

So, how many generations are we talking about? Well, on page 155 they write: “This reduction in predation pressure allowed the Chlorella population to recover and increase rapidly, …During the recovery of the algal population, an unexpected result was observed: the prey Chlorella now included colonial growth forms as well as unicells (10 days).”

So the unicells are grazed down for the first five days, and then in the next five days, ‘colonies’ appear. To get 20 generations into 5 days requires a growth rate of 6 hours. We know that’s wrong.

“Oh, but it’s not 5 days, it’s 10 days.” you say, since the Ochromonus was ‘introduced’ on the first day.

Well, then, what meaning shall we give to their acknowledgement that a “critical concentration” of the flagellates must be reached? Do the authors help us out? Of course not! But we’ve come to expect that by now.

Shall we assume the ‘critical concentration’ was reached in the first hours after inoculation? That seems completely unsupportable, but from their conclusions, that appears exactly what they reasoned. So here we have an issue that the authors bring up–the ‘critical concentration’ of an inducer–, but they do so without giving any explanation for it, and without demonstrating any effort on their part to determine if, indeed, such a concentration occurred, or when. We’re left dangling—as in almost everything in this paper.

Now, when did this possible ‘triggering’ occur. Well, if they want to ‘discount’ the possibility of chemical induction, then, as scientists, they should take the most conservative estimate possible of when, exactly, the ‘chemical trigger’ occurred. The most conservative estimate would be 7 days after inoculation (in papers on chemical induction in Scenedesmus, they say the response begins after 48 hours of introduction of the chemical inducer.) But certainly, after 5 days, at a time when the unicell density is very low and the Ochromonus is high, one can certainly say the ‘trigger’ has been signaled. So, that’s fairly conservative. Now, taking that conservative ‘time’ for the ‘trigger’, that leaves 5 days for the colonial forms to multiply and become evident. Well, how many generations does that represent? Do the authors help us? No, not really. But, after much difficulty, those posting here have come up with a number for the growth rate that is equal to the dilution rate. That number is 14.6 hours. But that 14.6 hours includes ‘wash out’ of some cells. The fastest time given on this post was around 10 hours (from memory: 9.9 hrs).

But there’s another factor to take into account. Boxhorn, one of the authors, writes on Talk.Origins.com, that the growth rate of strains that are competing for nutrient in a chemostat can be skewed depending on which form is dominating. And on page 158, in the legend, they write: “The majority of Chlorella cells were in colonies with more than 24 cells per colony for the first month of culture. The large colonies then disappeared from the culture and the number of cells per colony stabilized at eight.”

So, they first say that ‘colonies’ did not become apparent for about 20 Chlorella generations. But if the ‘multicells’ are dominant for the first month, then that means the growth rate of the ‘colonies’ will be less (perhaps much less) than that of the ‘multicells’. And since to ‘conservatively’ rule out chemical induction we’ve taken the 5-day mark as the time of the ‘trigger’; and since the authors tell us that on day 10 the ‘colonial’ forms were seen, that means that to determine the number of generations involved in the colonial forms appearance, we divide the 5 days by the growth rate. What growth rate should we take? I would say that it should be at least around the 14.6 hr/ generation mark. But to be ‘conservative’, let’s take 20 hrs. Then we’re looking at 6 generations—which is well within the range for chemical induction.

In one paper on chemical induction of Scenedesmus, the authors say that it takes 48 hours in the presence of the chemical inducer before anything happens, and that it takes 3-5 days (!!!) for the colonial forms to appear. So, in the paper at hand, if the ‘chemical inducer’ began to be produced after 3 days, then on the 5-day mark, the unicells would begin to react. And it would take them 3-5 days to appear. Translated, this means that by the 10 day mark the colonial forms would be expected to be present—which is, of course, exactly what the authors of the Boraas paper report. And why (if you deny that this was not an important fact to report, then you’re in complete denial) didn’t the authors tell us what was going-on on Day-8? Were the colonial forms already present? Why don’t they tell us, one way, or the other. This paper, in NO WAY, ‘discounts’ chemical induction.

I’m tiring of all of this. I could easily go on and point out that what we see is best explained as a ‘mother cell wall’ phenomena; and to point out that ‘multicellularity’ is never really achieved or arrived at [although it’s the authors main thesis. At best, the cells just simply ‘cling’ to the mother cell walls, which themselves cling to one another]. But as I say, I tire of all the nonsense on this board.

I’ll just leave you with this quote from a 2004 review article: (Plant Physiology, January 2004, Vol. 134, pp. 1—2,)

“Colonies of Chlamydomonas and Chlorella spp. stimulated quorum sensing-dependent luminescence in Vibrio harveyi, indicating that these algae may produce compounds that affect the quorum sensing system in Vibrio species.”

And this quote from a 2003 review paper: (Phenotypic plasticity in the green algae Desmodesmus and Scenedesmus with special reference to the induction of defensive morphology, M. Lürling; Ann. Limnol. - Int. J. Lim. 39 (2), 85-101)

“In fact, in culture unicells may be very common (e.g. Hegewald 1982, Holtmann & Hegewald 1986, Lürling & Beekman 1999, Trainor 1998), even at cell density far above ca. 1000 cells.ml-1. Hence, low cell density (Egan & Trainor 1989b) does not seem a prerequisite for unicell development in several Desmodesmus and Scenedesmus strains. And why are there that few reports of unicellular Desmodesmus and Scenedesmus from the field ? One explanation could be that due to the activity of grazers unicells are produced only in very low numbers, which experience a high mortality ; protective colonies are being induced. Trainor (1979) observed that unicells disappeared when incubated in dialysis sacks in the field or when cultured in pond water in the laboratory. Interestingly, in another study ten years later the same strain produced unicells in water from the same pond (Egan & Trainor 1989b,d). Perhaps the activity of grazers had been involved in this plasticity and grazer-associated chemical cues might account for the different observations by Trainor (1979) and Egan & Trainor (1989b,d). Also colonial D. abundans from the field formed unicells in the laboratory (Fott 1968). Another reason may be that unicells are simply not recognized as Scenedesmus. Opening a textbook one will find Desmodesmus and Scenedesmus presented as «a freshwater colonial green alga» often supported with images of four-celled coenobia. Unicells may resemble species described in at least eight other green algal genera (Trainor 1998). Kessler and co-workers using sequence analyses of 18S rDNA showed that two taxa of the unicellular Chlorella were in fact unicellular Scenedesmus while one Chlorella and one Kermatia had to be designated to Desmodesmus (Kessler et al. 1997)!!!!

Adieu.

PvM Wrote:

I’d like to hear Blast explain why Darwin was wrong about varieties and incipient species? And why should we rely on Denton whose book seems in many aspects to be quite flawed.

Because ‘chihuahuas’ aren’t about to form a ‘new species’ of Canus familiaris.

And, of course, Pim, that’s what all evolutionists say to criticism of their hallowed theory: it’s wrong; it’w flawed’ they don’t know anything about evolutionary theory, blah, blah, blah.

And Lenny, if you think that Denton contradicts himself in his “Nature’s Destiny”, I can only conclude–once again–that you’ve read neither one of them. You’re flat out wrong. Not every review you read on the internet–just because it appeals to you–happens to be factual.

Finally, the derivations of Anton and David Wilson both look fairly good.

I’ve looked at some papers on mixed species chemostats that deal with the mathematics, and they’re quite complicated. I think your equations, though simplified, are helpful. (Maybe I should say that BECAUSE they are simplified, they’re helpful–a compliment.)

Blast Wrote:

I’m very disillusioned with the attitude of the people on this board—and that includes you, Pim.

You all seem to lack any ability whatsoever to admit that there might be problems should those problems tend to undermine, in any way at all, the hallowed Darwinian orthodoxy.

Wow, that’s quite a jump from showing that your ‘irrefutable evidence’ hardly matched that description and was mostly based on a confusion as to what the authors actually argued.

So why are you creating this strawman argument?

In fact, even if you were right, I fail to see how this would undermine evolutionary theory?

Other than that Blast’s ‘response’ is not much different from earlier attempts, blaming others including the authors of the paper for his confusion and calling this a ‘serious problem’.

PvM Wrote:

I’d like to hear Blast explain why Darwin was wrong about varieties and incipient species? And why should we rely on Denton whose book seems in many aspects to be quite flawed.

Because ‘chihuahuas’ aren’t about to form a ‘new species’ of Canus familiaris.

And, of course, Pim, that’s what all evolutionists say to criticism of their hallowed theory: it’s wrong; it’w flawed’ they don’t know anything about evolutionary theory, blah, blah, blah.

Another fascinating strawman. Just because many of your ‘criticisms’ were found to be ill conceived does not mean that any and all such criticism is flawed’.

Why not focus on your claim about Darwin. How and why do you believe Darwin was wrong and how is your ‘example’ relevant? After all we do know of examples of speciation. Are you perhaps confusing Darwin’s explanation of how speciation happens with his ideas about speciation?

And Lenny, if you think that Denton contradicts himself in his “Nature’s Destiny”, I can only conclude—once again—that you’ve read neither one of them. You’re flat out wrong. Not every review you read on the internet—just because it appeals to you—happens to be factual.

ROTFL now that’s irony at work.

Btw it’s “canis familiaris”

And note how Blast seems to ignore the other reasons given why the authors reject the induction hypothesis. Somehow Blast took one, called it the ‘principal reason’ and avoids dealing with the overall reasons presented.

Irrefutable indeed…

Pim-

you do of course, realize that your simply feeding his delusions by the simple act of responding to them, yes?

The one thing I’ll give Blast over Larry is that he rarely spreads himself to other threads once focused on a particular non-issue.

logic levels are about the same, tho.

Careful Blast you are only a few day away. APRIL FOOL, n. The March fool with another month added to his folly.**

Why is it whenever the noose tightens you project ? Evolutionist this.….. evolutionist that. Your absolute classic was DarwinistsCreationists have been denying creationismevolution for 150 years.

Why align yourself with such an intellectually vapid and sine nobilis bunch of cultural miscreants ? A fringe group of knowledge pygmy’s ? Uneducated cultural slobs who think religion IS culture. ? Frightened that their hold on reality as described to them around 5 years old was just an elaborate fantasy. Wasting their lives and those of others justifying the unjustifiable.

Your should start your own eduKational intuition Blast , you have no need of knowledge.

The fact that two ‘taxa’ of Chlorella have been shown to actually be Scenedesmus, which is known to form a 8-cell colonial form through chemical induction, doesn’t seem to slow you down one bit, does it? Just pretend I never pointed it out.

Good-bye, Panda’s Thumb.

I don’t know if blast will ever read this, but I’ll post it anyways. Besides, other people may learn stuff.

I’ve allowed myself, let us say, a ‘cooling off period.’

I’m very disillusioned with the attitude of the people on this board—and that includes you, Pim.

You all seem to lack any ability whatsoever to admit that there might be problems should those problems tend to undermine, in any way at all, the hallowed Darwinian orthodoxy.

Our attitude might be more positive if you would show any propensity to argue in good faith. Instead, you continue to deliberately misconstrue the arguments made in the paper and by the people posting on this board.

PvM Wrote:

Hmm, I assumed you had read the paper “The cells in these stable colonies of predated cultures were enclosed within an envelope (Fig. 1d), apparently the mother cell wall of the neonatal cells (see Discussion). Empty mother cell walls were virtually absent from the culture.”

Yes, I’ve read the paper more than once. And I also read, “The most probable initial mechanism for colony formation, adhesion of the daughter cells to the mother cell wall, is suggested by two observations: the membrane that surrounds the colonies (Fig. 1d) and the absence of cast-off mother cell walls in cultures dominated by colonial morphs (personal observation).” So, which is it? Are they ‘virtually absent’, or are they ‘absent’, period? Wouldn’t it be nice to know?

First of all, since “virtually absent” is used first, it takes precedence. Secondly, the absence of mother cell walls is a “personal observation” which means the observation is not meant to be formal data. When you look at their methods, they were objectively determining the amount of cells of various sizes via the Celloscope, but not the number of empty mother cell walls. It appears that mother cell walls were only reliably detected with direct (microscopic) observation, which used smaller sample sizes than the Celloscope. Therefore, since the unicells were present at .1% of their initial levels, we would expect the cast-off walls to be present at a similarly reduced rate. Which means that instead of a visual field teeming with these empty cell walls, we would only rarely see a cell wall - they are virtually absent.

But I must confess, this particular argument of yours seems exceedingly pointless. For either of our models to be internally consistent, low but non-zero levels of empty cell walls (proportional to the unicell density) need to be present during the steady-state unicell-colony-predator chemostat.

This points out a serious problem with this paper: inconsistency in reporting and terminology. Where were the peer-reviewers?

As I say, it’s a serious problem.

The only problem is the artificial problems you are creating by deliberately misreading and misconstruing the paper.

We’ve already gone round and round on this: but what, exactly, constitutes a “multicell”? On one page of their paper they call it a ‘colony’, then it’s a ‘multicell colony’, and then they talk flat out about ‘multicells’. Why can’t they get their terminology consistent? Again, where are the peer-reviewers?

Their terminology is consistent - colonies and multicells are synonymous. You are trying to force a dichotomy that isn’t there. The failing is on your deliberate attempt to create problems that don’t exist on baseless assumptions.

They’re also inconsistent in their reasoning.

For example, what is their reason for ‘discounting’ chemical induction? The principal reason given is that: “First, colonies did not become apparent for about 20 Chlorella generations after inoculation of the flagellates. An ‘induction’ should have been expressed as soon as the inducing substance produced by the flagellates had reached some critical concentration.” (p. 159) Yet, on the SAME PAGE, they write: “In a system where environmental conditions were held constant, a multicellular organic form evolved from a unicellular one within 10±20 generations.” Well, again, which IS IT: 10 or 20 generations? When it comes to their MAIN reason for discounting chemical induction, they equivocate! Amazing!

They give four reasons. They do not have to be in any particular order of preference. They make no claim to it being their main reason, just one of four. And the other three are devastating to your induction hypothesis - you are picking on what may be the weakest argument. But setting that aside, there is a difference between the time to appearance of colonies and the time to evolve. It was approximately 20 generations before the colonial form started appearing in their microscopic scans. That does not mean that it wasn’t present before then, just that it wasn’t present in densities large enough to be noticeable in small sample sizes. My own interpretation of their use of evolve is that selection for colonies didn’t begin until 10-20 generations, rather than a mutation event occurring somewhere during that time period (though I don’t rule that out).

So, how many generations are we talking about? Well, on page 155 they write: “This reduction in predation pressure allowed the Chlorella population to recover and increase rapidly, …During the recovery of the algal population, an unexpected result was observed: the prey Chlorella now included colonial growth forms as well as unicells (10 days).”

So the unicells are grazed down for the first five days, and then in the next five days, ‘colonies’ appear. To get 20 generations into 5 days requires a growth rate of 6 hours. We know that’s wrong.

Actually, we don’t know that 20 generations into 5 days is wrong (and again, you have your units wrong - growth rate is in units of inverse time). We have repeatedly informed you that determining growth rate from flow rate only works during steady-state, non-predatory conditions. The growth rate will definitely increase during the first 8 days, at the very least. We haven’t determined the actual max growth rate of Chlorella, but what we have found through a literature search is that the minimum generation time is less than or equal to 8 hours. That gives us 6-7 days for 20 generations, but is not definitive.

“Oh, but it’s not 5 days, it’s 10 days.” you say, since the Ochromonus was ‘introduced’ on the first day.

Well, then, what meaning shall we give to their acknowledgement that a “critical concentration” of the flagellates must be reached? Do the authors help us out? Of course not! But we’ve come to expect that by now.

Shall we assume the ‘critical concentration’ was reached in the first hours after inoculation? That seems completely unsupportable, but from their conclusions, that appears exactly what they reasoned. So here we have an issue that the authors bring up—the ‘critical concentration’ of an inducer—, but they do so without giving any explanation for it, and without demonstrating any effort on their part to determine if, indeed, such a concentration occurred, or when. We’re left dangling—as in almost everything in this paper.

Simple examination of the data from Figure 2a shows that the Ochrimonus population had in fact peaked by Day 1. The data given supports the conclusion that a critical concentration was indeed present a few hours after inoculation - call it 12 hours, as that corresponds to twice the doubling time (given as 6 hours in the paper). The relative populations sizes don’t appear to be able to sustain an initial population boom of much more than that. The data is right there for us to see.

Now, when did this possible ‘triggering’ occur. Well, if they want to ‘discount’ the possibility of chemical induction, then, as scientists, they should take the most conservative estimate possible of when, exactly, the ‘chemical trigger’ occurred. The most conservative estimate would be 7 days after inoculation (in papers on chemical induction in Scenedesmus, they say the response begins after 48 hours of introduction of the chemical inducer.) But certainly, after 5 days, at a time when the unicell density is very low and the Ochromonus is high, one can certainly say the ‘trigger’ has been signaled. So, that’s fairly conservative. Now, taking that conservative ‘time’ for the ‘trigger’, that leaves 5 days for the colonial forms to multiply and become evident. Well, how many generations does that represent? Do the authors help us? No, not really. But, after much difficulty, those posting here have come up with a number for the growth rate that is equal to the dilution rate. That number is 14.6 hours. But that 14.6 hours includes ‘wash out’ of some cells. The fastest time given on this post was around 10 hours (from memory: 9.9 hrs).

First of all, Figure 2a clearly shows that Ochrimonus density is at a minimum at Day 5, not a maximum! Boraas et al even pointed this out. Perhaps you misread the paper yet again. The data is clear - if there was a critical concentration, it occurred within the first day. And where on earth are you getting “after 48 hours” from? Of the half dozen papers on colony inducement in Scenedesmus I was able to look at online, they all stated that within 48 hours colonies were the dominant form. Not just appearing, but dominant. BTW, the steady-state generation time (based solely on flow rate) is just under 14.3 hours (the growth rate is properly 0.07 h-1). But, as stated numerous times previously, the actual growth rate during these initial stages will be faster (the quickest generation time as posted here was estimated at about 8 hours, from other literature).

So the most conservative estimate based on real data would be 1 day (max concentration) + 2 days (time to dominate) = 3 days. We should see some sort of peak in Figure 2a sometime in Day 1-3, but we don’t.

But there’s another factor to take into account. Boxhorn, one of the authors, writes on Talk.Origins.com, that the growth rate of strains that are competing for nutrient in a chemostat can be skewed depending on which form is dominating. And on page 158, in the legend, they write: “The majority of Chlorella cells were in colonies with more than 24 cells per colony for the first month of culture. The large colonies then disappeared from the culture and the number of cells per colony stabilized at eight.”

So, they first say that ‘colonies’ did not become apparent for about 20 Chlorella generations. But if the ‘multicells’ are dominant for the first month, then that means the growth rate of the ‘colonies’ will be less (perhaps much less) than that of the ‘multicells’. And since to ‘conservatively’ rule out chemical induction we’ve taken the 5-day mark as the time of the ‘trigger’; and since the authors tell us that on day 10 the ‘colonial’ forms were seen, that means that to determine the number of generations involved in the colonial forms appearance, we divide the 5 days by the growth rate. What growth rate should we take? I would say that it should be at least around the 14.6 hr/ generation mark. But to be ‘conservative’, let’s take 20 hrs. Then we’re looking at 6 generations—which is well within the range for chemical induction.

Again, colonies and multi-cells are synonymous. But your analysis is completely wrong. This is a chemostat. In order to avoid “washing out” the growth rate must be at least equal to the dilution rate (as determined by the flow rate and the volume of the chemostat), regardless of what any other population is doing. In order for a population to grow, the growth rate must be faster than the dilution rate. The most conservative estimate, no growth, is 14.3 hours/generation, or a growth rate of 0.07 gen/hr. In reality, since the population is growing, we would be looking at something more like 12.5 hr/gen, or a growth rate of 0.08 gen/hr, as a conservative estimate - which is pretty close to an estimate of 20 generations in 10 days. 20 hr/gen is right out. Again, flow-rate is only definitive for steady-state, it is merely a boundary for transient states.

Larger colonies should have slower growth rates than smaller colonies, but it appears that the larger colonies start out with higher absolute numbers. Once we reach steady-state (in terms of unicell-colony-predator populations), the growth rate of smaller colonies will then be slightly faster than the dilution rate, and the growth rate of the larger colonies will then be slightly slower than the dilution rate. This leads to a slow washing out of the larger colonies and corresponding increase of smaller colonies, at a rate determined by the difference in growth rates.

In one paper on chemical induction of Scenedesmus, the authors say that it takes 48 hours in the presence of the chemical inducer before anything happens, and that it takes 3-5 days (!!!) for the colonial forms to appear. So, in the paper at hand, if the ‘chemical inducer’ began to be produced after 3 days, then on the 5-day mark, the unicells would begin to react. And it would take them 3-5 days to appear. Translated, this means that by the 10 day mark the colonial forms would be expected to be present—which is, of course, exactly what the authors of the Boraas paper report. And why (if you deny that this was not an important fact to report, then you’re in complete denial) didn’t the authors tell us what was going-on on Day-8? Were the colonial forms already present? Why don’t they tell us, one way, or the other. This paper, in NO WAY, ‘discounts’ chemical induction.

I assume that you are referring to the 1993 Hessen & van Donk paper. I am at somewhat of a disadvantage, since I can’t seem to access that paper online, but from other papers that reference it that I can get access to, you seem to be misinterpreting it. For example, from the second paper you quote later in your post:

Lurling Wrote:

Hessen and Van Donk (1993) discovered the involvement of a chemical cue released from the zooplankton in stimulation of colonies. The addition of filtered medium from a Daphnia culture (2 % v/v) to unicellular Desmodesmus subspicatus populations resulted within two days in populations dominated by colonies, while the controls remained unicellular.

Other papers, including at least one by the co-author van Donk, all indicate that it is within 48 hours that the colonies become dominant. None of them indicate a 3-5 day waiting period for the forms to appear.

Figure 2a has the data for Day 8. The data shows that colonial forms were present in low but growing quantities, according to the non-visual Celloscope. However, presence and appearance are two different things. The appearance of colonial forms in the visual microscopic samples was not reliable until Day 10.

The paper makes four arguments as to why induction is discounted. Here is the paraphrase of why the discounted it.

1. In induction, colony formation occurs and dominates quickly. This was not the case for this experiment. 2. In induction, colony formation is proportional to the density of the inducing substance. In the experiment, colony formation was independent of the flagellate density (for density>0). 3. In induction, colony formation is dependent on the continuing presence of the inducing substance. In the experiment, colony formation was independent of the continued presence of the flagellate. 4. In induction, colony formation is independent of available resources. In the experiment, colony formation was dependent on available resources.

The results of the experiment were consistent with known selection models and inconsistent with known induction models. Ergo, the induction model is discounted. Future experiments may someday discover an induction model that satisfies these requirements, but until then, the selection model is preferred due to its efficacy.

I’m tiring of all of this. I could easily go on and point out that what we see is best explained as a ‘mother cell wall’ phenomena; and to point out that ‘multicellularity’ is never really achieved or arrived at [although it’s the authors main thesis. At best, the cells just simply ‘cling’ to the mother cell walls, which themselves cling to one another]. But as I say, I tire of all the nonsense on this board.

Most of the nonsense is coming from you, blast. We are merely pointing out the obvious errors. If multicellularity is not achieved, what is your definition? Differentation is not being claimed here. Merely inheritable traits that cause multiple cells to cling together. And no-one disagrees (AFAICT) that the phenomenon involves the mother cell walls. What do you think the selection argument is trying to claim? Your objection is puzzling.

I’ll just leave you with this quote from a 2004 review article: (Plant Physiology, January 2004, Vol. 134, pp. 1—2,)

“Colonies of Chlamydomonas and Chlorella spp. stimulated quorum sensing-dependent luminescence in Vibrio harveyi, indicating that these algae may produce compounds that affect the quorum sensing system in Vibrio species.”

No one is disputing that induction happens. We’re just disputing that induction is happening in this case.

And this quote from a 2003 review paper: (Phenotypic plasticity in the green algae Desmodesmus and Scenedesmus with special reference to the induction of defensive morphology, M. Lürling; Ann. Limnol. - Int. J. Lim. 39 (2), 85-101)

“In fact, in culture unicells may be very common (e.g. Hegewald 1982, Holtmann & Hegewald 1986, Lürling & Beekman 1999, Trainor 1998), even at cell density far above ca. 1000 cells.ml-1. Hence, low cell density (Egan & Trainor 1989b) does not seem a prerequisite for unicell development in several Desmodesmus and Scenedesmus strains.

And why are there that few reports of unicellular Desmodesmus and Scenedesmus from the field ? One explanation could be that due to the activity of grazers unicells are produced only in very low numbers, which experience a high mortality ; protective colonies are being induced. Trainor (1979) observed that unicells disappeared when incubated in dialysis sacks in the field or when cultured in pond water in the laboratory. Interestingly, in another study ten years later the same strain produced unicells in water from the same pond (Egan & Trainor 1989b,d). Perhaps the activity of grazers had been involved in this plasticity and grazer-associated chemical cues might account for the different observations by Trainor (1979) and Egan & Trainor (1989b,d). Also colonial D. abundans from the field formed unicells in the laboratory (Fott 1968). Another reason may be that unicells are simply not recognized as Scenedesmus. Opening a textbook one will find Desmodesmus and Scenedesmus presented as «a freshwater colonial green alga» often supported with images of four-celled coenobia. Unicells may resemble species described in at least eight other green algal genera (Trainor 1998). Kessler and co-workers using sequence analyses of 18S rDNA showed that two taxa of the unicellular Chlorella were in fact unicellular Scenedesmus while one Chlorella and one Kermatia had to be designated to Desmodesmus (Kessler et al. 1997)!!!!

And the point of this (other than demonstrating that you already knew that induction occurred within 48 hours) is what? It does not support your induction claim. Best as I can tell, it demonstrates that the cladistics for algae were wrong because the cladists didn’t realize the plasticity of certain algae’s forms.

Adieu.

Somehow, I doubt it.

The fact that two ‘taxa’ of Chlorella have been shown to actually be Scenedesmus, which is known to form a 8-cell colonial form through chemical induction, doesn’t seem to slow you down one bit, does it? Just pretend I never pointed it out.

Demonstrate that this particular species of Chlorella is actually Scenedesmus. But that would be even more devastating to your argument, since the characteristics of the known inducements for Scenedesmus are contradicted by the evidence.

Kevin and Pim have refuted most of Blast’s closing arguments–though several of those arguments more or less refuted themselves. (Chlorella colonies aren’t multicellular, they’re just a bunch of cells that stick together? We’re entitled to ignore peer-reviewed articles if they contain synonyms? I see…) There’s just a couple of things I wanted to add.

First, although it’s already been pointed out several times, the Scenedesmus chemical induction phenomenon Blast referenced was cited in this very paper (Hessen & Van Donk 1993 was the initial study published on it so far as I can see) and provides the very example of induction Boraas et al. contrast against their own observations! The authors’ four arguments against induction were provided precisely to show that these two appearances of colonialism are not attributable to the same mechanism. Why Blast went to the trouble of finding more papers on Scenedesmus when no one’s disputing that that phenomenon really is induction, I’m not sure.

Second, one of the above anti-induction arguments is that the Chlorella colonies took much longer to appear after the flagellate’s introduction (20-100 generations) than we would expect if they were chemically induced. Blast counters that that duration can be accounted for if you add in some extra time while the colonies “multiply and become evident:”

So, they first say that ‘colonies’ did not become apparent for about 20 Chlorella generations. But if the ‘multicells’ are dominant for the first month, then that means the growth rate of the ‘colonies’ will be less (perhaps much less) than that of the ‘multicells’. And since to ‘conservatively’ rule out chemical induction we’ve taken the 5-day mark as the time of the ‘trigger’; and since the authors tell us that on day 10 the ‘colonial’ forms were seen, that means that to determine the number of generations involved in the colonial forms appearance, we divide the 5 days by the growth rate.

Unfortunately, this stuff about growth rates is pretty much useless for explaining the observations under an induction model, because you wouldn’t need to wait for the colonies to multiply in order to see them. In an evolutionary scenario, the growth rate would matter–all colonies will be descended from one or a few mutants, so you have to wait around while that small population grows large enough to be spotted. But in an induction model, lots of unicells are each giving rise to colonies–that’s the whole point of induction, after all! It doesn’t matter how slow the colonies reproduce; there should be plenty of first-generation colonies, immediate descendants of unicells, to be evident under the microscope.

So Blast’s explanation fails, and the the long duration before colony appearance remains good evidence (along with the true breeding of colonies, and the independence of colony number from flagellate density, and the suppression of colonies when the culture was darkened) that this wasn’t induction.

Wow, is the thread really over? I’m almost regretful…

Jebus! I can’t believe this crap went on for a month or more!

Will someone please explain to me how, if the Chlorella were becoming a new species, did it become the same species over and over again?

IOW, when the single-celled species was put under the same pressures, it rapidly evolved into a brand new species, and did it repeatedly 70% of the time.

Is this an accurate description of what happened, in your opinion?

First, I don’t know if the differences are enough to truly classify it as a separate species. It’s one of those fuzzy areas in biology when it comes to these types of critters.

Secondly, we haven’t determined whether this is a series of identical (or similar) mutation events that has arisen in most of the experiments, or if this is a persistent subpopulation that is below detection levels. The data as given supports both hypotheses. If the first, it would indicate that the mutation leading to colony formation is quite easy to obtain, which to me points to either a single point mutation or the wild-state being unstable but highly selected (ie multiple sites where a mutation can lead to colony formation). I think I’d favor the unstable explanation, as it better explains the multitude of colony sizes at first.

I think I’d favor the unstable explanation, as it better explains the multitude of colony sizes at first.

As would I, for the same reason. Evidently many different mutations were possible, given the initial explosion of colony sizes, so it seems unlikely that only one of them would result in 8 cells. Indeed, it’s hard to think of any phenotypic change that could only be accomplished by one possible mutation. If nothing else, codon redundancy means that two or three different mutations could result in precisely the same protein. And since a couple of fairly simple physical changes were responsible for multicellularity–incomplete breakdown of mother cell walls and adhesion of daughter cell walls–it’s likely that there’s many related proteins that could pull those off.

The “variable morphologies” of the 8-celled colonies also suggest that the genetic mechanism for multicellularity wasn’t exactly the same in every lineage. And if there was a pre-existing permanent 8-celled population, we would expect it to take over immediately upon flagellate introduction, rather than only appearing after a couple of population crashes and the subsequent appearance of various other colony sizes.

Jason, the reason the Chlorella ended up evolving into what was, at least to our eyes, very similar morphs* 70% of the time, was that they were subjected to exactly the same selection pressure each time. Anything with under eight cells got eaten, anything with eight cells or more was predation-free, but anything with over eight cells was much worse at taking up nutrients. So there was a very strong selection pressure each time for the same sort of phenotype, no matter what particular mutation caused it.

You see a similar phenomenon in human malaria resistance. There’s a bunch of mutations which confer resistance to malaria, and they all work differently–but since the malaria parasite lives in red blood cells, most of them affect those cells somehow. As a side effect of that, they tend to cause anemia. So even though we don’t expect the same precise mutation to arise every time, it’s a good bet that a human population that’s lived for a long time in a malaria-prone region will have a high incidence of some kind of genetic anemia.

*Like Kevin says, “species” are hard to define for asexual organisms, although I’d be happy to call this a new species. They’re typically defined on much less blatant morphological differences than this, plus the colonial and unicellular population can stably live side by side, forming an ecosystem with the flagellate. Should each 8-celled variant be considered a different species if it’s genetically distinct? Probably not, simply because then we’d have to call almost every asexual lineage a separate species. Better to reserve the term for when a genetic difference is accompanied by a significant morphological and ecological shift.

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This page contains a single entry by PvM published on February 13, 2006 10:00 AM.

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