# Evolution in Lake Tanganyika



## karatejo (Apr 10, 2003)

I thought I would start up a separate post for this also as Iâ€™d like to start up a discussion here
letâ€™s see how long it lasts 8)

http://www.cichlid-forum.com/phpBB/view ... p?t=179358

See below

The only matter I donâ€™t agree with in this documentary is the narratorâ€™s assertion that all life evolved in Lake Tanganyika independently from the Ocean because.... "Life there has lived and evolved under similar conditions". There are ocean like shells in the lake including crabs that would not look out of place in the sea and even its own type of sardines?....If a creature evolves into something resembling a crab then one might say that it looks like a crab....but it cannot be a crab.....similarly pretty shells cannot therefore be shells......and what of the sardines? 
As the Lake has a fairly high salt and mineral content and a fairly high PH...It is therefore my assertion that the lake was indeed once connected to the ocean even via maybe a small river? This may have been many thousands or even millions of years ago...so therefore we could not argue that it is not at least possible? The lake apparently has silt deposits of up to 3 miles thick! What is to say in some dark depths do not lurk the hidden mouths of some ancient caves that were once connected to the seaâ€¦.as is the case in in Yucatan Mexico? This would certainly explain how many types of marine resembling animals got into the lake in the first place and indeed arenâ€™t Cichlids supposed to be related to sea fishes? Animals evolving into identical forms from completely independent sources on one scale would be a miracle in itself but how several species are supposed to have evolved into the same animal types is quite frankly impossible absurd and against the very laws of evolution...animals evolve always from a common source of ancestry...animals rarely evolve identical forms on opposite sides of the planet from completely independent sources, which is why rare and strange animal types in areas such as Australia and Madagascar have animals indigenous to those areas because they evolved in isolation...if a lake had been isolated for so long such as Tanganyika then I would not expect to see similar life forms there that resemble ocean animals....

Comments please


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## blairo1 (May 7, 2006)

> Animals evolving into identical forms from completely independent sources on one scale would be a miracle in itself but how several species are supposed to have evolved into the same animal types is quite frankly impossible absurd and against the very laws of evolution...animals evolve always from a common source of ancestry...animals rarely evolve identical forms on opposite sides of the planet from completely independent sources,


Two words for you bud.... convergent evolution..... Fingerprints are a brilliant example of this. It's certainly not against any laws of evolution - evolution favours a successful mutation/adaptation and in similar environments, there will be similar, if not identical solutions.

I think you'd find George Barlows book - The Cichlid Fishes: Natures Grand Experiment, fascinating. In it he discusses how the land masses moved and naturally during these events species migrate to areas that eventually become cut off, how they then went on to evolve and the similarities and differences between them.

http://ib.berkeley.edu/labs/barlow/book.html

It really is a fantastic book and sounds like you might enjoy it (well written as a "breaking in" book).

:thumb:


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## xalow (May 10, 2007)

I second the recommendation for Barlow's book, its an interesting read.

Blairo1's mention of convergent evolution is spot on. Nature replicates certain patterns in unrelated species over and over again. This occurs all the way down to smaller subsystems such as the pattern of veins being similar to tree roots, or the end of a fern and a snails shell both being perfect logarithmic spirals. As Blairo1 all ready stated


> there will be similar, if not identical solutions


 you can look at how a bird such as the penguin has similar swimming profile to the very unrelated seal. Even the long extinct pterodactyl has wings that resemble those of bats.


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## BenHugs (Jan 13, 2007)

Well I think there is a totally different explanation here. People are said to have originated in africa and so I feel that the floods that Noah built his ark for also covered the great rift lakes letting sea creatures in and stranding them. :thumb: (lake malawi even has blue dolphins  )


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## blairo1 (May 7, 2006)

I like your thinking outside the scientific box, although I might be tempted to put the more religious aspects aside for a moment, you bring up a good point. One may want to look into the time frame involved , but that's not really something to delve into right here or now. 

I certainly believe there was a flood, as records show, but we also have proof of speciation and by using genetic sequencing we can actually back-trace the genetic lines (which is what is happening at the moment with some real breakthroughs). This is how we are coming to know the lineage of the fish. Ben I really suggest you read Barlows book with an open mind, it is such a well written book that anyone interested in fish will enjoy it and really take something from it. I hope you don't take this as me saying your views are wrong, I just encourage different thought and I think you'd really appreciate learning the background of our fish from a different viewpoint.

:thumb:


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## toddnbecka (Oct 23, 2004)

Keep in mind that all fish, inverts, etc. found in freshwater started out in the ocean way back when. Their ancestors migrated to freshwater environments, but they still carried the original genetic codes. In environmental conditions somewhat similar to the ocean they would have evolved into a closer resemblence to their marine counterparts than the ones that encountered significantly different conditions.


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## BenHugs (Jan 13, 2007)

blairo1 said:


> I like your thinking outside the scientific box, although I might be tempted to put the more religious aspects aside for a moment, you bring up a good point. One may want to look into the time frame involved , but that's not really something to delve into right here or now.
> 
> I certainly believe there was a flood, as records show, but we also have proof of speciation and by using genetic sequencing we can actually back-trace the genetic lines (which is what is happening at the moment with some real breakthroughs). This is how we are coming to know the lineage of the fish. Ben I really suggest you read Barlows book with an open mind, it is such a well written book that anyone interested in fish will enjoy it and really take something from it. I hope you don't take this as me saying your views are wrong, I just encourage different thought and I think you'd really appreciate learning the background of our fish from a different viewpoint.
> 
> :thumb:


Hey blairo1 I was not trying to to change anyones opinions here just having some fun with the flip side of this argument. I think if you believe in either creation or evolution there is no doubt that creatures do evolve to thrive in thier environments. I'll have to take a look at this barlows book you suggested.


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## blairo1 (May 7, 2006)

:thumb:

I'm into this topic because I'm studying evolution of fish for my ichthyology course, so I'm all up for hearing some different viewpoints!

Here are some interesting thoughts:

Primitive fish are generally thought to have initially evolved in the sea. So how do other concurrent species of freshwater fish come to simultaneously be distributed through such varied geographical areas?

Then there are the arguments:


* Abandonment of marine habitat by marine orders?
* Moving from SW to take advantage of resources existing in FW 
* The fish were migratory - preferring to live in SW but migrating into FW in order to make use of resources eg. spawning habitat or food availability
* With the similarities in habitat found in each geographical region the preferred assumption is that the current structure is a result of past land connections or proximity of land masses
* The existence of Primary FW families lends credence to the theory that FW fish evolved inland and dispersed when land masses were joined and became isolated when land shifted
* The sheer movement of continents through time

The outcome of evolution is also deeply influenced by competition and interaction between species, so there is a strong non-deterministic component resulting from 'accidents' of distribution.

One also has to weigh in factors such as the effects of:


* A change in habitats over long periods of time
* Movements of plates into new climatic zones 
* 1000's years of drought in some areas or ice in others
* Freshwaters are also susceptible to changes in drainage, emptying lakes, reversing rivers etc

The main factor in the comparative lack of diversity from some communities of freshwater fauna is due simply to the unpredictability of conditions. The oceans fauna has always been able to migrate whilst land moved and therefore have evolved in a relatively constant set of conditions. Fish distribution is also subject to various geographical factors such as physical barriers - permanent mountain ranges, and temporary barriers such as those caused by glaciation. One also needs to think about the fauna itself and its physiological tolerances and ecological adaptations.

These processes have produced habitats (and ecosystems) which resemble each other over similar geographical areas. When species find stable environmental conditions, it tends to lead to adaptive radiation / speciation. Obviously the similarities in environment will naturally lead on to convergences in the faunas adaptations to suit such environments.


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## RyanR (Apr 29, 2008)

I'm more a fan of the natural history of four-legged critters (I *love* New World cichlids too!), but I'll hazard a few guesses based on what I know about some of this stuff.

The answer has a lot to do with biogeography driven by plate tectonics... and the story *has* to go back at least to the "Age of Dinosaurs" (before Africa, Antarctica, and South America broke up last). African and New World cichlids share a common ancestor, and no cichlids are truly saltwater. Thus, the cichlids had to have split up before the land connections between those three continents were severed... which was pretty well a done deal by 65 million years ago. This gnoshes well with that we have sparse cichlid fossils in South America dating back 30-40 million years.

The African rift lakes are remnants of a failed "attempt" to rip a big chunk of Africa off of the rest of the continent as the plates were pulling apart, but the the area that became the Red Sea was the weaker link... That rip in Africa is also pretty ancient... I think within the last 65 million years, but I don't know for sure... and I'm too lazy to look it up. 

The failed rifting created a pretty serious gouge in the continent, and all of that sediment fell into what became the lakes. Water likes to pool and travel in such deep gouges and imperfections. I don't know if those lakes got salty from either a connection to the sea or leaching out of underlying geology... or some other phenomenon.

Based on what I know of New World cichlid relationships, I'll hazard another guess that that the cichlid family originated either in southernmost South America (prolly not) or Africa (I like that story better) and dispersed one direction or the other across Anarctica. It definitely appears that New World cichlids originated in the south and diversified towards the north (Central American cichlids are evolutionarily more "recent" than South Americans).

Then the world gets cold in the last 40 million years, and Antarctica goes from "not bad" to "stupid cold" as the circumantarctic current sets up, and erases what I bet is an important part of cichlid evolutionary history... which if preserved in the fossil record is buried under a whole lot of ice....

Of course, take this with a grain of salt... I'm out of my element. :lol: 
-Ryan


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## dwarfpike (Jan 22, 2008)

Something to make your brain hurt:

If lake tang fish developed completely independantly in any way, none of the fish in it could be cichlids. Cichlids are by deffination secondary freshwater fish, meaning their ancestors did indeed start in the ocean and come inland.


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## BenHugs (Jan 13, 2007)

I would like to mention as well that the rift lake crabs, snails eels etc......... all seem to look a lot like sea creatures to me


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## Guest (Sep 16, 2008)

You guys are misinterpreting what the narrator said in the documentary. He said that Lake Tanganyika was never part of the Ocean or Sea, which is true. It is a freshwater lake.

Eventually if you go back far enough everything in Lake Tanganyika has its ancestors coming from the oceans, but no direct (recent) ancestry. When the continents were together the cichlid ancestors were all over the tropic areas of Pangea (for example, many of Madagascar's cichlids are in fact direct Jurassic cichlids and didn't change much at all in the 65 million years or so).

One would assume that fresh water snails are descendants of saltwater at some point hundreds of millions of years ago, but to say that the fresh water snails and crabs and turtles migrated from the ocean to the lake recently is ridiculous.

Take a look at this article by the way by Paul Loiselle about Jurassic Cichlids: http://www.cichlidae.com/article.php?id=97

~Ed


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## blairo1 (May 7, 2006)

> Eventually if you go back far enough everything in Lake Tanganyika has its ancestors coming from the oceans, but no direct (recent) ancestry. When the continents were together the cichlid ancestors were all over the tropic areas of Pangea (for example, many of Madagascar's cichlids are in fact direct Jurassic cichlids and didn't change much at all in the 65 million years or so).


 :thumb:


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## BenHugs (Jan 13, 2007)

Marduk said:


> You guys are misinterpreting what the narrator said in the documentary. He said that Lake Tanganyika was never part of the Ocean or Sea, which is true. It is a freshwater lake.
> 
> Eventually if you go back far enough everything in Lake Tanganyika has its ancestors coming from the oceans, but no direct (recent) ancestry. When the continents were together the cichlid ancestors were all over the tropic areas of Pangea (for example, many of Madagascar's cichlids are in fact direct Jurassic cichlids and didn't change much at all in the 65 million years or so).
> 
> ...


I agree marduk
I mentioned the snails, crabs etc...... as a remark that the lake could have had "ties" to the ocean at one point in the past and not have evolved ocean like creatures on its own. (which is how I took some of the conversation above was implying)


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