[Cyprinodontiformes] Participação no fórum GWG

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Caros colegas,

Mais uma partilha de informação.
Desta vez a minha primeira intervenção no fórum internacional do GWG :


GWG Feb-26-11 10:07:22
Variation within species and selection within our strains

Dear all, 

I remember that one of you wrote about a difference in tail colour in Ameca (whitish
versus yellow band). I also notice this in my fish, with the addition that not only
the tail colour differs but also the colour of the whole body: my impression is that
some fish are much less depositing carotenoid colours in their skin and fins than
others. In juvenile fish this difference is not so clear, but the adults are
dimorphic. Bothe females and males are either "greenish" or "greyish", in the latter
case males have a whitish band in the tail in stead of bright yellow. 

I assume that this difference has a genetic basis. In the long term, I expect that
one of the varieties will take over, because of coincidence or maybe because of a
preference for partners of one of the varieties.

I wonder what to do. In my small group it might be impossible to maintain both
varieties, but I could, for instance, selectively remove one of them. Supposedly the
group would then, after some generations, become homozygous for the remaining
variety. 

I would actually like to discuss this more in general: a species has several colour
varieties (in the case of Ameca, there is the "dark" variety and apparently also a
yellow/greyish variation - I presume that the latter are independent of "dark"). 

Do we have to aim to maintain all the varieties? In that case it might be sensible to
set up separate strains of each variety, even if they occur in mixed populations in
nature.

This, of course, would mean more administration and more aquariums needed. 

The alternative is to keep them together, but this means a high risk to lose some of
them because of the combined effects of inbreeding and genetic drift. 

I think that we should distinguish between the "slight and apparently natural
variations" which I like to discuss here and the obvious mutations like albinismm,
which would in nature have lowered survival and which we can also safely cull, or
maintain as "aquarium curiousity" but which are not very relevant to species
conservation.

Paul

___________________________________

Feb-26-11 13:42:44

Hi Paul, 

A difficult but important question... We have different colour varieties in
tale-bands (mainly in yellow-orange or yellow-white) in tank-bred populations, but
probably also in the habitat. As I have the impression, Goodeid-males often play with
contrasts (yellow with black band or orange with dark body also). Maybe these
contrasts are more important in male choice than absolute colours. In my tequila
group a few years ago, I had yellow and orange tailed males and both had been mating
successfully. On the other hand, colour variations in small groups (or small tanks)
might to lead to problems through an aberrant looking dominant male (could be
aberrations hidden in females too, but that would lead too far at the beginning of
this discussion, I presume). Me, for my part, I would like to have the
captive-populations looking as similar to wild populations as possible, so I think in
some species (Ameca splendens would belong of these species), I would advise to keep
them in bigger tanks and bigger groups, starting with 250 liters to provide too much
influence by one dominant "macho". In a lot of other species, there seem not to occur
many variations in colour pattern, so I see this problem restricted to some species,
either longterm kept in captivity or variable from nature. However, I would prefer to
have "my populations" look like the wild, so I wouldn't try to keep different
colour-strains to increase the genetic diversity, but that is absolutely worth to be
discussed  

Best, Mike

Michael Köck

___________________________________

Mar-03-11 22:20:03

I wonder if we should aim for maintaining overal genetic variation (if at all
possible) or at maintaining fenotypic variation in each tank. I doupt that the latter
is possible without occasional exchanges of fish. Even if there is not a single
dominant male, i suspect that one variety might be more attractive to the females
than the other, meaning that gradually the population in each aquarium could shift
towards that variety.  

Like in guppies there is strong female preference for bright coloured males, which is
in nature balanced because the brightest coloured males are also having most risk to
be eaten by predators. Therefore the outcome of female selection + predation is not
the same as female selection + human selection. 

Maybe the question should be if we should have some kind of registration of varieties
(within population!) as well, to avoid accidentally losing some of them.

___________________________________

Mar-05-11 00:25:35

Hi Paul,

It was me the one who have notice two different colours in Ameca splendens' tail
band.
This was not a simple variation inside the same group of fish but either a
distinction between two independent lineages.
In both cases all males exhibit the precise tail band tone.
The "German strain" ( because it was imported from Germany and the original
population it was unclear ) had a almost whitish tail band.
The "Czech strain" ( because it was imported from Czech Republic and the original
population it was unclear ) had a very canary yellow tail band.
Other very noticeable differentiations were some behavioural features and males
intraspecific aggression.
If you wish any further details, please be may guest.

Best regards

Miguel Andrade