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
To: Nicholas Thompson
Cc: Hugh Trenchard ; 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 covertrole 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 wontsay more,
now. Nick Nicholas S. ThompsonEmeritus 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
AppliedComplexityCoffee 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 offitness > between the strongest and weakest riders. In contrast, think
of a packof > runners of varying fitness levels. There is negligible drafting
effect - > there is some, esp if running into a headwind, but overall it's
smallenough > that it can be ignored for this illustration. Say there are 50
runners,all > separated incrementally by 1% difference in fitness; say they run
acouple > of miles. If they all start off slowly at say the max speed of
theslowest > runner, they can all run in a big group, separated only by
enoughdistance > 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 separatedincrementally &!
gt; by d
istances that correspond to their differences in fitness. In thespace > of two
miles, they all finish individually in a single long lineaccording > 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 cansave > at least 25% by drafting (approx savings
1%/mph) - all theriders 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. globallycoupled > by finishing within drafting range of each
other), and so theparadox. Part > of the paradox is also that, while fitness
levels are effectivelynarrowed > 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
clearfrom > my initial post (though it is certainly implied). Also, thereare
other > important things going on in a peloton which precede the sorting
ofriders > 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
pelotonrotations, > and 2) points of instability when riders are forced into
positionswhere > 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
withinthe > peloton, and in this particular phase, a self-organized
rotationalpattern > 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 leastas >
high), cross-winds, narrowing of the course, or short anaerobic burstsamong >
riders at the front - all of which cause splits (i.e. PDR>1 atthese > 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 whichstronger > riders are able to get to
the front and the continual splits in thepeloton > 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 abasic > 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 quiteincorrectly), > that there is
some initial phase in which they are mixed (such ascyclists > on a starting
line), and then they begin to sort as they increasespeed. > During the process,
they aggregate like cyclists because a broader rangeof > fitness levels can
aggregate together (causing an effective narrowingof > 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 amongthe > 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
theanswer > 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! ButI > do
remember that scene from the movie as clear as day!>> In any event, my aim is
really to ask the question - are there energeticand > 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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