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PostPosted: Sat Mar 11, 2006 11:38 am 
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A personal view....

DNA might not be a certain guide to species (remember the birds that develop different songs, and so split off - their dna would have been identical), but it has to be a very big factual clue!

It depends how you define species I suppose. I can imagine too that very minute, perhaps almost undetectable, genetic differences could cause significant colour differences that gain would cause groups to stop inter-breeding.

We like to categorize our fish rigidly, but the fish don't care a hoot. My guess is that evolution is far more dynamic than most people think, with lots happening in a short time - when conditions are ripe (new territories, new threats, new water conditions, new food sources, etc etc.)

I do hope that the new study of angelfish that was metioned a short while ago includes a structured collection plan, with on the spot recording & the rest. Otherwise all the real dynamics of the process could be overlooked.

Alec


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PostPosted: Sat Mar 11, 2006 12:23 pm 
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Yes, that´s right. With it I can correspond. We must let all work on it to expertly ichtyologists. And be waiting ... waiting ... waiting and be patient. :cry:

Jan

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PostPosted: Sat Mar 11, 2006 11:57 pm 
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Picked up another snippet this last week. About some migratory birds that migrated to different areas for the winter.
They only paired with other birds that migrated to the same area as themselves.
Suggested to be the start of the splitting process, with the different groups diverging thereafter.
Unfortunately I can't remember where it came from (might have been the radio) and a couple of searches I just did drowned me in bird flu reports.
Alec


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PostPosted: Sun Mar 12, 2006 2:29 am 
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Problems with species by rainbowfishes are also interesting. There are possible crossing of species between them. I know from my friends,which make rainbowfish, that they must be very careless. There are not problem interbreeding species in genus Melanotaenia and make so "new" (false) species.
Yes, it´s difficult situation - where are borderlines?

Jan

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PostPosted: Sun Apr 16, 2006 5:05 pm 
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I've been studying evolution for quite a few years now and I don't think I'll ever get bored with it. Defining a species has always been a debated issue in the field and I think it always will. For me I'm more interested in the process and what promotes evolution. It can happen very rapidly, I mean there's a different flu shot every year, antibiotics are becoming ineffective, insects become resistant to pesticides, these are all examples of comtemporary evolution. Fish are no exception to this, just look at all the varieties of angels, they're really examples of comtemporary evolution that are the result of artificial selection on various traits.

As for what's occuring in nature from natural selection check these arctic charr out. They're from Thingvallavatn, a lake in Iceland which is less than 10,000 years old. These fish can all interbreed when humans intervene but in nature each has their own set spawning time. The biggest one is predatory on small charr and sticklebacks, the little one below it lives in cracks and crevices of the lakes lava rock bottom and feeds on small snails and chironamids (bloodworms), The silver one lives out in the open water and feeds on plankton, the big one on the bottom lives off of large snails and lives in the benthic/profundal zone of the lake. Genetically, fish from this lake are more closely related to one another than similar forms from other lakes.


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PostPosted: Mon Apr 17, 2006 10:35 am 
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There are lakes near here where char are found. Those lakes were created at the end of the last ice age, about 11000 to 12000 years ago.
The char in our lakes are small fish, like a small trout weighing maybe up to 250 grams or so.
They typically live in the deeper parts of the lake, below 30 metres.

When I was a teenager I used to go fishing in those lakes and caught many trout, but had no luck with the char though I only really tried hard once to catch them in a place where the water is >30m deep at the edge of a lake.
Most of the trout were natural wild fish. Their flesh was typically pink, though in quite varying degrees.
Typically the trout I caught would weigh about 600 grams, though there are some much bigger ones there that are usually referred to as cannibal fish.

It's easy to see how the feeding habits of fish could lead to speciation. Those living and feeding at different depths would tend to experience spawning triggers such as temperature and light at different times, and so could eventually form a separate breeding population.
Also feeding on different foods just by itself could give different levels of conditioning that would put the fish in spawning condition at different times.

I guess the big difference between natural selection and artificial selection is that on is selected almost entirely on the basis of survivability and the other on the basis of the human perception of such factors as 'beauty' or 'food production potential' in the fish!

I find it a fascinating subject too.

Alec


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