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 allow 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 questions, 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 group thins into a line and are separated >incrementally >> by distances 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 fitness 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 >> occur 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 >> the principles apply to each aggregation. However, I don't know whether >> 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 >> > >
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