----- Original Message -----
From: John Bongiovanni
Sent: Wednesday, March 05, 2003 9:30 PM
To: nanfa_at_aquaria.net
Subject: Re: NANFA-- Louisiana sinking and other thoughts
It's fairly certain that sea levels have changed over time mostly due to
fluctuations in polar ice. My question was based upon two assumptions.
1) that dramatic changes in sea level resulted in changes in salinity
and 2) that teleosts radiated from FW to salt and back. That the
fluctuations in sea level provided a vehicle for that radiation. My
first assumption has pretty well been shot down. Ouch! But maybe not
completely inacurate. The second one has a little more muster.
I like to envision the events that causecontribute to disjunct
distributions of fish like the distributions of The Mississippi Silvery
Minnow and the segregations of the percina and etheostoma genera.
Maybe changes in the salinity of the sea is more localized rather than
globally. The MSSM, according to petersons has a distribution
throughout the Mississippi valley and along the gulf coast drainages to
the Brazos River. Then it jumps several hundred miles down to the Rio
Grande. The two most likely events I can imagine that account for this
distribution would be a temporary change in sea level that allowed
migration of ancestral populations north or south as the case may be
and/or reduced salinity in the Gulf due to heavy flooding. The flooding
temporarily forced fresh water into the gulf thus allowing migration to
other drainages. If a population gets a "finhold" in this new
distribution the population could genetically isolate itself from the
ancestral populations overtime with the help of random mutations and
bottleneck events.
The differences between the Percina and the Etheostoma appear pretty
clearcut. Phylogenies nowadays can be generated fairly easily by the
use of DNA analysis. Certain judgements must still be made in regards
to the lumping or splitting arguements. What is less clear are the
events that lead up to or contributed to establishment of the unique
populations we call species. Were the progenetor etheostomas fish that
found more succcess in the shallower portions of the water table? And
those with smaller swim bladders more successful in this new niche?
Did they crowd out other species because they could draw on their
ability to frequent both the benthic portions of the stream as well as
higher portions of the water column? As they crowded out, out competed
the resident populations were they then able to specialize into the
species we knwo today? How
Of course, I keep coming back to the same question: how did we wind up
with Darters in the St. Lawrence system as well as in the Trinity and
Brazos sytems in Texas? There has to be a conduit that allowes the
migration of the species to dramatically jump to different river
drainages. Was the common ansestor of the Percina and Etheostoma
brackish or salt adapted first and then radiated into the different
drainages?
Well, I guess if we could answer all those questions with certainty we
would be writing books and not e-mail!
John
Todd Crail wrote:
>Thanks for piping in Luke. I think that's a valid point, and one that I
>won't even touch as I'm not a palentologist, just a fully fledged
>speculativist :) There's prolly a bunch of different ways to argue that
>matter, all of which based on observable and "proofable" concepts... I think
>more of the point for our purposes is to discover how past melting of polar
>caps etc had affects on salinity and the consequent movement of species to
>utilize the new situations.
>
>That, and to give John something else to think about when he's wallowing in
>a muddy mess the next time ;)
>
>So I hope I've not completely railroaded the conversation into the
>"terminal" :)
>
>----- Original Message -----
>From: "Michael Canady" <canady1538_at_msn.com>
>To: <nanfa_at_aquaria.net>
>Sent: Wednesday, March 05, 2003 9:43 PM
>Subject: Re: NANFA-- Louisiana sinking and other thoughts
>
>
>
>
>>Just to let everyone know out there
>>-the astroid theory is obsolete now according to my biology profesor at
>>washington state university. Fossil evidence shows that the dinosaurs
>>
>>
>took
>
>
>>around a million years to die out, not days, or weeks, but lots of time,
>>
>>
>and
>
>
>>why did the astroid kill the dinosaurs, but not the early mammals of the
>>
>>
>time?
>
>
>>-luke
>/"Unless stated otherwise, comments made on this list do not necessarily
>/ reflect the beliefs or goals of the North American Native Fishes
>/ Association"
>/ This is the discussion list of the North American Native Fishes
Association
>/ nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word
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-
/"Unless stated otherwise, comments made on this list do not necessarily
/ reflect the beliefs or goals of the North American Native Fishes
/ Association"
/ This is the discussion list of the North American Native Fishes Association
/ nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word
/ subscribe, unsubscribe, or help in the body (not subject) of an email to
/ nanfa-request_at_aquaria.net. For a digest version, send the command to
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/ For more information about NANFA, visit our web page, http://www.nanfa.org
/-----------------------------------------------------------------------------
/"Unless stated otherwise, comments made on this list do not necessarily
/ reflect the beliefs or goals of the North American Native Fishes
/ Association"
/ This is the discussion list of the North American Native Fishes Association
/ nanfa_at_aquaria.net. To subscribe, unsubscribe, or get help, send the word
/ subscribe, unsubscribe, or help in the body (not subject) of an email to
/ nanfa-request_at_aquaria.net. For a digest version, send the command to
/ nanfa-digest-request_at_aquaria.net instead.
/ For more information about NANFA, visit our web page, http://www.nanfa.org