Peter, I'm glad you jumped into this, and nailed most of these already...and
Chris, your species stuff is dead on.
If anyone would rather spend time in a lab writing up species descriptions
than be out playing in the field, they're seriously warped. Really. If
anything, spending time in the field and getting confused about
identifications should be an incentive to look closer.
Breeding experiments aren't the answer, some folks have been looking-in-just
how choosy male darters are when taken out of allopatry, and the answer is
they often aren't (see Mendelson 2003). Heck, some miscreants even managed
to get hybrids between Texas logperch and orangethroat darters (Hubbs and
Strawn 1957) - fish do weird things when you take them out of their natural
environment.
>>I find it really hard to hold that there aren't "intergrades" or zero
>>interaction in a single watershed inbetwix Ulocentrids (thus creating
>>two separate species), no matter how different the geology is where
>>they're found.
...but the assumption that because two things look superficially alike that
they're closely related is not always valid, either. If two taxa aren't each
other's closest relative, then a little bit of occasional hybridization is
moot. Yeah, sure, you might get occasional hybrids- but the long-term effect
of these is generally minimal. Much of what's driving this is allopatry by
drainage, and you can certainly hop from one drainage to the next and get
different critters in each.
>>I mean really, I spent three days last week standing somewhere in
>>between the edge of the basin, on the barrens, and-in-the base of the
>>rim, and I'm not really sure where these "species" start and end, let
>>alone where the physiogeography of these _streams_ starts and ends.
Yeah, it's a remarkable area. In some cases the physiography is blatant (try
visiting Old Stone Fort SP just SW of Manchester TN), in other cases they
kind of blend into one another. Vegetation covers up much of the interesting
geology. Like I mentioned earlier, what matters isn't <our> inability to
identify the break, it's that there's really some difference there that
causes one species to drop out and be replaced by another, and that can be
really obvious.
>Sounds like a good phd to me! :-) If you are into species boundaries and
>what prevents movement of genes across those boundaries. Fascinating
>stuff me thinks.
I totally agree. Steve's genetic data didn't recover each "species" as
monophyletic, but if these things are recently derived you might not expect
full coalescence of each lineage. Heck, in some ways that makes the story
even more interesting. If you look-in-the ability of these fishes to move
back into areas after droughts, it's remarkable. They have the latent
ability to disperse far and fast. Something is keeping them from doing
so...so what is it? Are other taxa that share the same geographic
distribution similarly constrained?
A couple years ago Larry Page came up with an idea about competition
actually driving isolation. At the time I laughed it off and thought it was
a crackpot idea, but lately it's been sounding a little more plausible, and
at the very least it could be a pretty cool hypothesis to test against real
data.
Nuts, that means more time in the lab and less in the field...
cheers,
Dave
-- wish I were out dragging a bag seine rather than in front of a computer...
--------- for the really bored:
Hubbs, C. and K. Strawn. 1957. Relative variability of hybrids between the darters, Etheostoma spectabile and Percina caprodes. Evolution 11(1):1-10.
Mendelson, T.C. 2003. Sexual isolation evolves faster than hybrid inviability in a diverse and sexually dimorphic genus of fish (Percidae: Etheostoma). Evolution 57:317-327.
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