Hugh -- I like the analysis very much. There should be other cases of velocity sorting in microbiology and perhaps in developmental biology, any place where cells are potentially crowded and need to get some where.
I think that sustainability for sperm is an oxymoron -- they have fixed food reserves and run until they succeed or starve. Fitness is probably the wrong word, too, you can frame this in terms of individual and group efficiency: the "peloton" goes further and gets anywhere sooner than any of its individuals could do by itself. So the doggerel version of the proposal would be able to start with: "promiscuous peromyscus spermatozoa". Perhaps Doug can get over his brightly colored spandex fixation and finish it for us? -- rec -- ** On Mon, Mar 29, 2010 at 9:42 AM, Hugh Trenchard <[email protected]> wrote: > Thanks Eric for taking the time to look through my post. For Nick's last > post, I am not entirely sure what a "genefur" is, although it sounds like it > is a reference to an inherent genetic trait, as you also discuss. > > Yes, I agree it will help my argument if I hone in more closely on what I > mean by fitness, and I will add some description to clarify this. My useage > relates to inherent physical fitness in terms of maximum power output > capacity. That too needs fine-tuning because I refer to "maximum sustainable > output", which is not the same as absolute maximum power output, and I would > need to outline more carefully what this means. Regardless, I think there > are ways of testing for the actual power-output capacities of individual > sperm - I have seen references in the literature to testing procedures for > this. > > Because I know very little about genetics, for my part I would be treading > dangerously to begin describing the process in a gene-related sense (and > I would not want to get into discussion about chromosomes), but to address > the issue you raise (if I understand it correctly), it would be necessary to > measure the power output of the sperm of individual male mice to determine > the range of their output capacities and/or the sperms' average output. This > is no doubt not easy, but I imagine there would be some sampling size that > would provide an accurate indication of the overall output range. And > certainly one would want clearly to correspond average sperm outputs and > ranges with the genetic descriptions of the various mice tested, but this > could be done according to a replication of the Fisher and Hoesktra > procedures. It would also be necessary to determine percentages of energy > savings that occur when sperm are coupled (if this does in fact occur). > > My model assumes that there is a difference in the average power output of > individual males' sperm, whether related or unrelated or of the same species > or not - a difference sufficiently significant to demonstrate that sorting > occurs according to fitness (in the power-output sense) and not according to > some mechanism for identifying the genetic relatedness of the sperm, as the > authors of the Nature article appear to suggest. The fact that sperm > aggregate indicates coupling and energy savings, which is why (in my view) > the peloton model applies. > > In terms of chance, it seems to me Fisher and Hoekstra have taken a lot of > care to establish that there is sorting beyond chance, but implicitly > ascribe that sorting to some sensory/perceptual capacity of the sperm to > identify related sperm. My model begins with their proven result that there > is sorting beyond chance, and asks whether there is some > sorting mechanism involved other than an unidentified mechanism to perceive > the location of related sperm, which is intuitively problematic because (it > seems) sperm do not have a sufficiently developed sensory system (i.e. eyes, > ears, or other) to do this. > > My model provides a simpler explanation for the sorting process than the > Hoekstra & Fisher explanation, because, in my model, sorting occurs > according to self-organized energetic principles, and not according to a > perceptual/sensory mechanism, as apparently implied by the authors. > > I can see how a basic computer simulation would be helpful as a starting > point for making predictions according to my model, which I see is really my > next step. > > Does anyone know how/where one could apply for some funding to resource > such a simulation? I could develop it myself (and have developed at least > one simulation, but it really needs to be worked through again), but it > would happen a whole lot faster if I could engage someone more adept at > computer modelling than me. > > > ----- Original Message ----- > > *From:* ERIC P. CHARLES <[email protected]> > *To:* Nicholas Thompson <[email protected]> > *Cc:* Hugh Trenchard <[email protected]> ; [email protected] > *Sent:* Saturday, March 27, 2010 2:54 PM > *Subject:* Re: [FRIAM] Sperm pelotons; article in Nature > > Hugh, > Very interesting model! One of my doctoral adviser's, Jeffrey Schank has > demonstrated repeatedly that scientists are very bad at predicting what > 'chance' looks like when trying to do experiments involving synchrony. This > seems one of those situations, and the only way around it is modeling. > > Nick's sarcasm aside, he has a point, and it has to do with some of the > flavor text surrounding your model (for geeks of the wrong variety to know > what flavor text is, see: http://en.wikipedia.org/wiki/Flavor_text). If I > can take a shot at identifying the problem: > > Rather than looking at 'fitness' as if it were a unified trait, you have > created a model that needs some mutli-stage selection language (the better > term escapes me at the moment). The reality is that what makes a 'fit' sperm > is not necessarily what makes a 'fit' organism. To fix the flavor text of > your model, you would need to explicitly recognize that (if the sperm sort, > then) the sperm are going to sort based on a similarity in the genes that > 'build' the sperm. Their sorting will be completely independent of all the > other genes, or of any role that the sperm-building genes might later play > as body-building genes. Ignoring chromosomal linkages (which you shouldn't), > two sperm could be identical on all the genes important for building sperm, > but completely different in terms of all other genes. > > Your model would thus al! low a much clearer test of the prediction that > sperm identify each other in some way. It does so because it provides a > vastly improved predicted relatedness due to chance. GIVEN: We would expect > sperm to cluster along the race track based on the similarity of certain, > specifiable genes. MODEL: If we know the genes important for building sperm, > we can model the expected relatedness of sperms within a cluster. IF: Sperm > are implementing some weird sort of kin selection mechanism - THEN: we would > expect the relatedness to be significantly larger that what our model > predicts. > > Any help? > > Eric > > > On Sat, Mar 27, 2010 01:36 PM, *"Nicholas Thompson" < > [email protected]>* wrote: > > Hugh, > > Even if it has nothing to do with sperm it is a nifty model. > > There is an idea lurking here that i dont know whether it plays a covert > role in your thinking or not, but what about the fate of a "genefur" > peletonizing. > > My email program is misbehaving and my computer is about to crash so I wont > say more, now. > > Nick > > Nicholas S. Thompson > Emeritus Professor of Psychology and Ethology, > Clark University ([email protected]) > http://home.earthlink.net/~nickthompson/naturaldesigns/ > http://www.cusf.org [City University of Santa Fe] > > > > > > [Original Message] > > From: Hugh Trenchard <[email protected]> > > To: <[email protected]>; The Friday Morning Applied > Complexity > Coffee Group <[email protected]> > > Date: 3/27/2010 10:54:41 AM > > Subject: Re: [FRIAM] Sperm pelotons; article in Nature > > > > Thanks for taking a peek at my post. Great que! > stions, and they help me to > > see how/where my descriptions can be clarified. > > > > On the paradox part - that is one of the really interesting features of a > > peloton: the energy savings effect of drafting narrows the range of > fitness > > between the strongest and weakest riders. In contrast, think of a pack > of > > runners of varying fitness levels. There is negligible drafting effect > - > > there is some, esp if running into a headwind, but overall it's small > enough > > that it can be ignored for this illustration. Say there are 50 runners, > all > > separated incrementally by 1% difference in fitness; say they run a > couple > > of miles. If they all start off slowly at say the max speed of the > slowest > > runner, they can all run in a big group, separated only by enough > distance > > between them to keep them from kicking and elbowing each other. As they > > pick up speed, the gr! > oup thins into a line and are separated > incrementally > &! > gt; by d > istances that correspond to their differences in fitness. In the > space > > of two miles, they all finish individually in a single long line > according > > to their fitness, and it can be predicted accurately where runners will > > finish if you know their starting levels of fitness. > > > > This is not the case with a peloton. For example at 25mph, riders can > save > > at least 25% by drafting (approx savings 1%/mph) - all the > riders who are > > within 25% fitness of the fastest rider can ride together even at the max > > speed of the strongest rider. So their fitness levels are effectively > > narrowed, and they can all finish together as a group (ie. globally > coupled > > by finishing within drafting range of each other), and so the > paradox. > Part > > of the paradox is also that, while fitness levels are effectively > narrowed > > by drafting, it means, conversely, that a broader range of fitn! > ess levels > > can ride together in a group, which maybe isn't something that is clear > from > > my initial post (though it is certainly implied). Also, there > are other > > important things going on in a peloton which precede the sorting of > riders > > into groups, some of which I see I do need to clarify to make my model > > clearer. > > > > Of these, particularly important are 1) the occurrence of peloton > rotations, > > and 2) points of instability when riders are forced into positions > where > > they do not have optimal drafting advantage. Below a certain output > > threshold, when all drafting riders in a group are sufficiently below max > > output, riders have sufficient energy to shift relative positions within > the > > peloton, and in this particular phase, a self-organized rotational > pattern > > forms whereby riders advance up the peripheries and riders are forced > > backward down! > the middle of the peloton. However, instabilities in pace > oc > cur along the way, caused by such things as course obstacles, hills > (when > > lower speeds reduce drafting advantage, but when output may be at least > as > > high), cross-winds, narrowing of the course, or short anaerobic bursts > among > > riders at the front - all of which cause splits (i.e. PDR>1 at > these > > points). In a competitive situation, instabilities occur frequently > > causing temporary splits at various places in the peloton, but these are > > often closed when the cause of the instability has ceased. Sorting thus > > occurs according to some combination of peloton rotations in which > stronger > > riders are able to get to the front and the continual splits in the > peloton > > at points of instability and reintegrations. I would need to develop the > > model some more to show this as an equation (though I touch on a > basic > > version of it in my Appendix). > > > > For sperm, I! > don't know what the initial state of the aggregates are when > > they begin their travels, but I am assuming (perhaps quite > incorrectly), > > that there is some initial phase in which they are mixed (such as > cyclists > > on a starting line), and then they begin to sort as they increase > speed. > > During the process, they aggregate like cyclists because a broader range > of > > fitness levels can aggregate together (causing an effective narrowing > of > > fitness). As in a peloton, there are instabilities that allow for > > continuous re-adjustments to the relative positions of all the sperm, and > > over time they begin to sort into groups where each have fitness levels > > closer to the average. This is my hypothesis, at least. > > > > On the second last question, there would be an advantage to sperm among > the > > first pulse aggregation if all the pulsed aggregations do not mix first, > but > &g! > t; the principles apply to each aggregation. However, I don't! > know wh > ether > > there is some other process of mixing first among all the pulses of sperm > > aggregations before they begin traveling (I imagine I could find the > answer > > in the literature), in which case there could easily be a sperm in, > say, > > the second pulse, which could end up impregnating the egg. > > > > I don't know about the kamikaze sperm - I'll leave that one for now! But > I > > do remember that scene from the movie as clear as day! > > > > In any event, my aim is really to ask the question - are there energetic > and > > coupling principles that allow sperm to end up in groups which otherwise > > appear to have occurred because genetically related sperm can somehow > > identify each other? I am really only suggesting the existence of some > > dynamics of the sperm aggregations that could be studied for, which don't > > yet appear to have been addressed. > > > > Hugh > > > > > ============================================================ > FRIAM Applied Complexity Group listserv > Meets Fridays 9a-11:30 at cafe at St. John's College > lectures, archives, unsubscribe, maps at http://www.friam.org >
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