Text 456, 159 rader
Skriven 2004-10-21 09:48:00 av John Edser (1:278/230)
Ärende: Pleiotropy Enforces Coope
=================================



I would like to thank Dr Guy Hoelzer
for bringing to my attention this seminal
paper.

---------------------- paper quote ---------------------------
Pleiotropy as a mechanism
to stabilize cooperation
Kevin R. Foster1*, Gad Shaulsky2, Joan E. Strassmann1,
David C. Queller1 & Chris R. L. Thompson2,3*
1Ecology and Evolution, Rice University, Houston, Texas 77005,
USA 2Department of Molecular and Human Genetics, Baylor College
of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
3School of Biological Sciences,University ofManchester,Manchester
M13 9PT,UK * These authors contributed equally to this work.

Most genes affect many traits1–4. This phenomenon, known as
pleiotropy, is a major constraint on evolution because adaptive
change in one trait may be prevented because it would compromise
other traits affected by the same genes2,4. Here we show that
pleiotropy can have an unexpected effect and benefit one of the
most enigmatic of adaptations—cooperation. A spectacular act
of cooperation occurs in the social amoeba Dictyostelium discoideum,
in which some cells die to form a stalk that holds the
other cells aloft as reproductive spores5,6. We have identified a
gene, dimA7, in D. discoideum that has two contrasting effects. It
is required to receive the signalling molecule DIF-1 that causes
differentiation into prestalk cells. Ignoring DIF-1 and not
becoming prestalk should allow cells to cheat by avoiding the
stalk. However, we find that in aggregations containing the wildtype
cells, lack of the dimA gene results in exclusion from spores.
This pleiotropic linkage of stalk and spore formation limits the
potential for cheating in D. discoideum because defecting on
prestalk cell production results in an even greater reduction in
spores. We propose that the evolution of pleiotropic links
between cheating and personal costs can stabilize cooperative
adaptations.
--------------------- end paper quote ----------------------------

JE:-
A slime mould slug is formed within nature
using the process of cell aggregation. Many
independent parental cell lines that can be derived from
different cell clones now merge to form
a single soma that can move about and produce spores
by settling and lifting a spore head into the
air on a long stalk of dead cells. About 1/5 of the cells must
sacrifice themselves to form this stalk which remains critical
for supporting the remaining 4/5 who alone are able to form
reproductive spores. Individual parental cells could have
formed spores on their own and not pay this risk. However, the
gains via aggregation allow each separate parental cell to
maximise their own Darwinian total fitness via cooperation.
I argue that  such an act of fitness mutualisation is totally
basic, even when the cells cooperating are not related.

The cost to each parental cell is the risk that it must die
to form the stalk. However the gains from slug formation
outweigh this risk as an individual parental investment
cost. This means that cells that never aggregated and
thus never risked 1 chance 5 of dying without reproducing
themselves by forming the stalk reproduced a fitness total
into one population that was absolutely _less_ than those that
did take this risk. Note that those that take the risk will
still be selected to compete against each other
to reduce their own risk that they must
form a stalk. However, if this selective contest reduces
the total investment in the stalk below a minimal value ALL
lose out because all will suffer a reduced total (absolute)
fitness when just a zero/a reduced stalk becomes formed.
Such  forms cannot compete against more highly mutualised
parental forms that do not make this error. Note that
no group selection or fitness altruism is ever involved.

It appears Pleiotropy for the same gene is critically
involved in evolving such a mutual fitness _safeguard_.
This acts to prohibit natural individual cell competition
within the slug, to minimise each parents risk in forming
the stalk, from reducing the total investment in a stalk
below a critical minimum so that all cellular parents
do not suffer an absolute fitness loss. Relative gains
in spore formation cannot be selected for if such gains
only result in a total (absolute) loss for the majority
of cellular parents. A Darwinian maximand cannot be selected
to be reduced. Spore formation is not a maximand but
fertile cell reproduction from spore formation, is.

Hamilton et al argue that organism fitness altruism
(OFA) can be selected FOR using Hamilton's rule:

	rb-c > 0

However the _total_ fitness of the actor was not included
because most of the fitness the rule needs to address
to prove OFA has been deleted as the missing "baseline"
fitness m:

      m + rb-c > m

While deleting m from both sides does not
alter the mathematics of just _relative_
measures it does drastically alter
the biology because OFA can only be _proven_
when the _total_ fitness of the actor can
be proven to be _selected_ to have been
_lowered_. It can be shown that just one
such case can be proven, when:

	rb-c > m

Since m remains deleted the rule cannot measure
the only definitive case of OFA that actually
exists.

Because the rule can only measure the relative difference
between rb and c via simple subtraction no measure can
exist for OFA using it. Thus I maintain that Hamilton's
rule has mistaken OFA for its opposite: organism fitness
mutualism (OFM) ever since its inception. All the rule
actually measures is that as long as the association is
OFM and not OFA, mutualised fitness associations between
relatives can evolve allowing more related genes
to be organism replicated than would have been the case.
However this is not a cause just an effect of a
Darwinian (and not a Hamiltonian) fitness maximand.
No gene level of selection has been proven to force
OFA at a supposed contesting organism level of selection
as Hamilton et al continue to incorrectly argue.

Fitness mutualisation is an enormous selective
force within nature. It is a part of the Baldwin
Effect. Sadly, fitness mutualisation has been almost
entirely ignored in favour of just mythical fitness
altruism by what appears to be a biased Neo Darwinist
establishment that remains obsessed with the concept of
fitness altruism existing within nature, against
any reasoned argument.


Regards,

John Edser
Independent Researcher

PO Box 266
Church Pt
NSW 2105
Australia

edser@tpg.com.au
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