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Re: Continued breeding of my Fp gardneri misaje population

>Lets postulate that everyone know a little of population genetics...
>
>> > >> Interesting stuff.  clearly if maintaining genetic diversity is
>> > >> what you want, breeding fish that are as distantly related as
>> > >> possible is always good. *within * species
>
>Genetic diversity is more than what can be summed up in a pr or
>group. It is a statistical assement of all the allells in the population.
>You can not hope to maintain the genetic diversity of a species or
>population by pulling a few fish randomly from it.


Well, a pair or a few fish in a collection represent a small population
that goes on to establish itself in our tanks. Whatever diversity that
population has in the original sample is what you have to work with.  One
of the points made somewhere in here was that given the small number of
individuals to start with that won't be much, no.  However, if the source
population's diversity is low (i.e. the population was small and inbred to
begin with) then the genetic diversity lost by taking a small sample will
not be great.

>With the exception of humanity
>which has spread accross the world in the relativly short time of 40
>odd thousand  years, most organsims have been firmly planted in
>the lace where they evolved. Killies are good examples. Take
>nothos for example. There are countless pools of the same specie
>of notho scatterred across the savanha. They are all so distinct
>that they often don't look the same (eg eggersi) this doesn't make
>them any less the same or distinct.
>If one asseses the genetic diversity of the species as a whole one
>could find a huge diversity but when comaring the diversiity at a
>population level you may find that there is almost none.
>It is much the same with Aphyosemions.
>In the June 1998 issue of TFH (i think) there was an article by
>Prof. Romand on Scriptaph. geryi. In one population he had
>previously assessed the colour pattern had changed completely in
>10 years. This population was in a small well or pool if I recall
>correctly.
>The point is: the phenotypes of the species can change greatly in a
>short space of time but not really effect the genetic diversity of the
>population. While the complete colout change may of occured it
>represents just one set of alleles which were present in the original
>population.

It appears we don't have any actual data on gene flow between
subpopulations, so it could be quite a bit higher than one might imagine
(it often is, which is why I say that). It's not clear why this would be
thought a phenotypic change without genetic basis.  It seems to me that if
you have a trait that isn't known to change with environment (you'd think
someone would have noticed if the color patterns depended strongly on
environmental conditions), and you see a big shift, it's likely the result
of some genetic change that's happened in the population over those 10
years.  That'd suggest there's more gene flow than one would think.

If so, the intial populations may be reasonably diverse leading one to
expect inbreeding depression



>How does one explain the decline in AUS productivity over the last
>few years? Has the calibre of hobbyist decreased so profoundly in
>last few decades?

>There are numourous strains of AUS in circulation not just the lump
>sum gold and chcololate AUS strains. Each strain seems to have
>different fucundities. My friend's pure gold strain is a never ensding
>source of trouble.  My other friend
>(who I got my fish from) has no problems [with his hybrid strain] The
>hybrid vigour is amazing.  We have
>seen no reduction in fertility.
>Inbreeding has an effect if continued long enough with out proper
>selection. As Wright pointed out, as the strain progresses the
>infertility genes do get spread out over the population causing
>reduction in fercundity.



Inbreeding has an effect, even if carried out with selection.  It isn't so
much that "infertility" genes get spread around so much as that the start
showing up in homozygous form, allowing them to be expressed.  You are
losing genes all the time, including "fetility" genes and the more
inbreeding the faster this proceeds.  Between losing good genes and
exposing new deleterious ones this is pretty much what you might expect
from an inbred line.  The fact that the hybrid has good vigor speaks to the
benefits of crossing less related strains within species.  Now, I'd lay
money that this wouldn't work with every species, since some probably are
highly inbred and may show outbreeding depression.

>> > The thing that's really odd about what you describe is that if the
>> > hybrids (the descendents of the oddball female) are less
>> > fertile/viable that less hybridized offspring gang spawning, or even
>> > selective breeding the best breeders, should lead to the loss of her
>> > genes pretty fast (if there's a big effect).

>> Real outcrossing/gang-spawning spreads her genes too quickly, when the
>> reduced fertility is delayed by several generations, as it often seems
>> to be. There is actually a tendency to "hybrid vigor," I think, that
>> spreads them even quicker.
>
>This principle is well displayed in maize farming. Monsanto etc...
>insert infertilty genes in their super productive seed. For the first
>generation the maize if fantasticly productivte but you try and get a
>harverst from the 3rd generation. The productivity has droped to
>1/4 of what is was. 1/8 th in the 4th etc...

The only problem is that if there's hybrid vigor, that means that her genes
weren't infertility genes since the fish that have them reproduce more, not
less.  If the *really* cause a reduction in fertility, then those fish that
have them won't be able to keep up and the genes are lost.  That's how
natural selection works.  In Monsanto's case the original productive corn
isn't actually fertile, so it'll set seed (which we eat) but it's not
viable seed.  Since the corn is genetically identical to begin with its not
resulting increased out breeding but just the consequence of having reduced
viability.

I missed this part, so I don't know what came from where, but how, when,
whether to cull is a really interesting debate.

>> Culling is a really bad idea when it isn't done by the fish
>> themselves. It inevitably leads to selection to please the
>> eye/esthetics of the breeder and will push the strain away from the
>> wild characteristics even faster than just putting them in tanks does.
>
>You make the error in presuning the wild characteristics are stable.
>Wild stock, to survive, has to be more labil and able to addapt.
>Altering colour in the aquarium can be seen as an extension of that
>lability. To survive the fish must look pleasing to the hobbyist. :-)
>
>Select for healthy fish: no bent backs fins etc...
>Select for productive fish.
>Select for colour if you like. If you want o keep the fish looking like
>the wild stock, ask someone to send you pics one a year and
>select accordingly.
>I would tend to select mainly for the intermediates (those that have
>the highest allele to genome ration) but keep oneor two extreme
>examples around just to keep the continuity going.

Well, Wright's correct on this one, but I think it's inevitable, since what
leads to success in tanks (probably the ability to deal with water changes
and with salt, for openers) is different than what works in the wild, so
selection is likely to shift the population from the wild traits.  There's
more to it than we can see from by eye.  It is probably true that many
traits change with environment, but the fish don't have it under conscious
control, so they can't just change to please us (oh, but if they could!)

That having been said, it seems that the upshot of all this is that
inbreeding will eventually erode all the diversity we have, leaving us with
nearly geneticall identical strains.  If we can *select* for genotypes that
can succeed when inbred, we may end up with some viable aquarium strains (I
don't mean aquarium hybrids, but highly inbred versions of the original
collections).

The other option would be to try to maintain species as big populations and
do a lot of outcrossing among the collections (probably) to maintain a
single very diverse population.  It should be pointed out that having a
whole set of highlyinbred strains also represents having a bunch of genetic
diversity, it's just not within strain.


So, if you are aiming to have highly inbred, "aquarium successful" strains,
then culling, perhaps with occasional outcrossing, would be the way to go.

If you are doing a genetic diversity maintenance regime, then the breeding
methods may be different.  Clearly, there will be some compromise between
these two aims.


>The fun with science is that any idiot willing to pick up a book and
>read can understand and eventually give commentary.

Anyone who spends years watching fish "do their thing " also knows a hell
of a lot about it, too!

>

>Kind regards
>Tyrone
>
>http://www.geocities.com/tyronegenade/intro.html
>***********************************************************
>
>"Submit to God and accept theword that he plants in your
> hearts, which is able to save you."
>                                   James 1:21
>---------------
>See http://www.aka.org/AKA/subkillietalk.html to unsubscribe


Doug Karpa-Wilson
Department of Biology
Indiana University
Jordan Hall
1001 E. 3rd St.
Bloomington, IN 47405


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