Re: NANFA-- ESC, populations, and genetics

Bruce Stallsmith (
Mon, 28 Feb 2000 09:23:14 EST

Martin, your question set here is an outline for a graduate level
biodiversity/evolution seminar, I'm impressed! Data exists on a bunch of
these questions, even if consensus doesn't necessarily.

>This whole shad thing has piqued my interest. I have to throw a
>question out there for you professionals. Do you think that
>genetically distinct populations of conspecifics should be afforded
>the same protection as a species? Are these populations really
>important, or is it a difference which _makes_ no difference? Is
>there any data to support either position?

Yes, genetically distinct species should be treated as distinct units, since
gene frequencies are measured & have an affect at the population level (a
species often being made up of multiple populations that can crossbreed).
Data exists to support this with the various salmonids, and also with the
mummichog, _Fundulus heteroclitus_, among others.

>Here's another one: Is there any data to show that two distinct
>populations have preferential (or otherwise population selective)
>reproductive habits? Are there any fishes which morphologically
>appear to be the same species, are able (and willing) to freely
>interbreed if given the opportunity to do so, and yet are classified
>as different species by DNA analysis?

Many anadromous fishes have distinct year-classes, or runs, that are
genetically distinct--esp. smolts and _Alosa_ shads/herrings. The second
part of this paragraph is hazier, since DNA analysis alone is not used for
species classification except for the various bacteria.

>Can there be as much genetic diversity in a common, large reservoir
>of individuals as in two smaller isolated groups? Data?

Yes there can be, although it's not necessarily a stable gene frequency
point (we skitter into the theoretical here). Chimpanzees have much more
genetic variation than humans do, which I suppose could be argued either

>Why do plants hybridize so frequently? Can a hybrid become
>established so as to be considered a seperate species? Is it
>possible for a hybrid to show more genetic "distance" from its
>parents than other species which are closely related to the parents?
> How is DNA analysis used to measure distinctiveness?

Plants have different chromosomal regulatory mechanisms, such that they can
build up multiple sets of chromosomes (polyploidy) or acquire extra
chromosomes that becomes a stable set through meiotic error (chromosomes not
separately cleanly during gamete formation). Offspring can be totally
separated reproductively from their parents because they have acquired
different genomes (chromosome counts & functions). Simply doing a karyotype,
a counting of chromosomes, allows much analysis.

>Is the genetic material in, say, an amoeba, a subset of that found in
>higher animals? I.E. are the genes themselves unique to amoebas,
>or is it simply that the combination of particular genes is unique?

Amoebas and other unicellular organisms have their own evolutionary
histories, with many genes unique to themselves. Our last common ancestry
with such protistans would be 1.5 - 2 billion years ago so they've had
plenty of time to develop new material.

>Sorry, I guess that was more than one question :-) Don't want to
>appear ignorant on this list, but this is important to my
>understanding/evaluation of the Evolutionary Species Concept.

Or most other Species Concepts, for that matter; Dave Neely's advisor/capo
di capos Rick Mayden has a paper out discusisng 23 species concepts, most of
which he doesn't like. (I'm still reading it Dave!).

In evolutionarily significant solidarity,
Bruce Stallsmith

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