Does anybody besides me have problems getting past the term "sperm pelotons" without having bizarre mental images of teeny little bicycles, spandex, and colorful itty bitty jerseys?
--Doug On Mon, Mar 29, 2010 at 9:42 AM, Hugh Trenchard <htrench...@shaw.ca> 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 <e...@psu.edu> > *To:* Nicholas Thompson <nickthomp...@earthlink.net> > *Cc:* Hugh Trenchard <htrench...@shaw.ca> ; friam@redfish.com > *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" < > nickthomp...@earthlink.net>* 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 (nthomp...@clarku.edu) > http://home.earthlink.net/~nickthompson/naturaldesigns/ > http://www.cusf.org [City University of Santa Fe] > > > > > > [Original Message] > > From: Hugh Trenchard <htrench...@shaw.ca> > > To: <nickthomp...@earthlink.net>; The Friday Morning Applied > Complexity > Coffee Group <friam@redfish.com> > > 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 > > > >
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