Re: orange flies

"Stan Gula" <sgula@xxxxxxxxxxxxxxxxxxx> wrote in
oy9bg.1922$nq5.943@trndny06:">news:oy9bg.1922$nq5.943@trndny06:

Scott Seidman wrote:
<snippage>
If trout can see into the UV, almost guaranteed that there was some
evolutionary pressure that pushed them that way, at least for some
period during trout natural history.
<and more snippage>

*OR* it was a random mutation and it was not disadvantageous so it
never got selected out. Like, for example, blindness in cave fish.
Which is what I presume you meant by 'almost', but couldn't resist
fleshing out.


Actually, I was thinking more along the lines of a crosslinked phenotype
that isn't advantageous, but comes along as a partner to some other
beneficial change. Try as I might, though, a good example isn't really
popping into my head. The closest I can think of right now is hybrid
sickle cell, which provides resistance to malaria, but but the pure form
can be deadly. This isn't quite what I'm looking for, though.

Funny you should bring up cave fish. My quick search shows there's
actually much debate on the topic

Romero et al., J Exp. Zool. 300B(2003)72-79
"The process leading to the reduction or elimination
of phenotypic features among animals living
in environments such as caves, abyssal zones, or
remote islands continues to be a source of
controversy. In the case of hypogean (cave,
artesian, phreatic) fishes, more than 150 years of
heated discussions have yet to definitively identify
the mechanism underlying such troglomorphic
changes when a population is isolated from and
then subject to selective pressures different than
its ancestors (Romero, 2001)."

See also
http://loom.corante.com/archives/2005/02/16/eyes_part_two_fleas_fish_and_
the_careful_art_of_deconstruction.php

So, the above link suggests that overexpression of this substance "Sonic
Hedgehog" (no ***!!), which causes the misdeveloped eyes, might be
causing adaptations that favor efficient feeding, and the eye thing is
just riding shotgun. Turns out to be exactly what I was trying to
describe above!! In the cave fish, because they don't need eyes, the
overall effect of the mutation is thus positive, but in the fish that
gets exposed to light, this mutation has a negative overall selective
pressure. So, this Jeffry guy suggests that in the case of the cave fish,
Darwin gave up on Lamarkian selection too quickly. This stuff was also
published in Science
(http://www.sciencemag.org/cgi/content/full/288/5474/2119)
which serves to demonstrate that there really is an ongoing argument
(Science mag leans toward the controversial).

Me, I'd posit that there is some positive evolutionary pressure for a
cave fish not having eyes, even without the other Hedgehog induced
changes. Neurons are about the biggest metabolic drains in the body.
Also, there's only so much brain (or whatever passes for a brain in
fish), so I'd suspect that in the genetically blind fish there is some
substantial brain remapping to put this tissue to better use. Apparently
the evolution guys disagree with me, but what do they know?


--
Scott
Reverse name to reply
.