From: toby@carson.u.washington.edu (Toby Bradshaw)
Newsgroups: rec.birds
Subject: Re: Peregrine Diet
Date: 13 Oct 92 16:08:57 GMT
Article-I.D.: u.1992Oct13.160857.6115
Organization: University of Washington, Seattle

In article <718528625.0@wyrm.rbbs-net.ORG> Joe.Morlan@f501.n914.z8.rbbs-net.ORG (Joe Morlan) writes:
>
>      ***** On 10-04-1992, Toby Bradshaw wrote to All *****
>
>TB> Since American kestrels were widely used to experimentally
>TB> study DDT effects on raptors, any genetic data would come
>TB> from that program.
>
>American Kestrels do not normally live long enough for residues
>of DDT to build up to toxic levels in their tissues.  Are there
>studies showing adverse effects of DDT usage in wild populations
>of American Kestrels?

Citation, please.  I know of kestrels at least 9 years old,
breeding well in captivity.  I don't know of any DDT studies
on wild kestrels.

>TB> I'm sure you realize that this is not evidence for genetic
>TB> resistance; only a suggestion that genetics is one of
>TB> several possibilities.
>
>What other plausible mechanisms can you suggest to account for
>the fact that not all Peregrines were equally effected by DDT?

If DDT levels were the same in fat, there could be a difference
in mobilization due to dietary intake of calories, for example.
What evidence shows that the putative "resistant" peregrines
had elevated tissue DDT levels, and that the high levels were
present for times known to cause eggshell thinning?

>TB> As for poaching, and egg collecting, and "unscrupulous
>TB> falconers" (they exist, like unscrupulous people in all
>TB> walks of life) causing the decline of peregrines: the same
>TB> pressures existed in Great Britain for centuries with no
>TB> significant decline until DDT use became widespread.
>
>The serious decline was caused by DDT, but the actual extinction
>of breeding populations was almost certainly caused by poaching.

Proof by assertion?

>I am convinced that wild populations would have been able to
>recover without the expense of captive propagation, if the
>successful breeding pairs had been left alone.  Is there
>plausible evidence to the contrary?

There were no or very few successful breeding pairs east of the
Rockies, just as brown pelicans were wiped out as a breeding
bird in California during the same period.  As far as I know,
brown pelicans came back on their own, as you posit for
peregrines.

>TB> If they are "resistant", why are their shells thin?
>
>Eggshell thickness is not the only factor affecting productivity.
>The composition of the shell itself is just as important.  E.g.
>if the shells are too porous, the eggs will fail regardless of
>thickness.

Still, if they're "resistant", why did they show adverse
effects?  Do you contend that there were successful eyries
in the 70s in NJ?  If so, I'd like to see the evidence
(since I don't know one way or the other).

>TB> But evolution only has genetic variation as raw material.  No
>TB> genetic variation, no evolution, period.
>
>Genetic variation is caused primarily by an inherent error rate
>in DNA replication.

Not necessarily.  Mutations arise in many ways.

>This error rate (molecular clock) ensures
>that there will be variation, therefore there will be evolution.

It doesn't ensure that in finite populations all mutations will
occur or be exposed to selection.

>TB> Maybe four eyes would have adaptive value for woodcocks, but
>TB> unless one is born that way, and the "four eyes" phenotype
>TB> has a genetic basis, there's no variation on the "two eyes"
>TB> theme, and no target for natural selection to favor "four
>TB> eyes".
>
>Evolution doesn't work this way at all.  A woodcock with four
>eyes is a hopeful monster.  It is no more a unit of evolution
>than a woodcock with two heads.

This argument is totally wrong.  Evolution can and does work
in just the way I've described.  The empirical evidence for
neo-Darwinian adaptive evolution in small increments is
weak, and there is pretty good evidence that speciation
(the major process of organic evolution) can be instantaneous.
There is a paper in press (H.A. Orr and J. Coyne, American
Naturalist) that nicely summarizes the available evidence for
both points of view.

Toby Bradshaw
Department of Biochemistry and College of Forest Resources
University of Washington, Seattle
toby@u.washington.edu
Newsgroups: rec.birds