Dear Gijs et al.,

There are basically two approaches to the scenario put forth by Gijs:
speciation by formation of stable, reproducing hybrids.

First there is inference from molecular phylogeny.  According to Tom E.,
such is apparently the case with Tom Eichhorst's New Mexican whiptail
lizard, Cnemidophoorus neomexicanus Lowe & Zweifel, 1952, which appears to
be hybrid between paternal C. inornatus and maternal C. tigris
marmoratus.  Obligingly, the ancestral taxa have survived to be
contemporary with the derived taxon (and allow tissue of all three to be
sampled).

The second is inference from the fossil record using careful analysis of
time (stratigraphy and/or physical or chemical geochronology) and fossil
morphometry.  In the case of the Mollusca, the first such study, and maybe
the only and maybe the best, was reported less than a decade ago.

Glenn Goodfriend and the late Steve Gould studied Pleistocene to Recent
(late Quarternary) remains of Cerion (Pulmonata: Stylommatophora) snails on
the shores of Great Inagua, Bahamas.  Using principally chemical indicators
of age, they were able to show the evolution of species mix involving two
sets of stocks.  In each an original taxon found to be established about
15,000 years ago was later joined by and invading species.  In one
scenario, the aboriginal form quickly disappeared, but an intermediate
(presumably hybrid) form appeared at the same time and persisted in
equilibrium with the invading species.  In the other situation, at some
distance (in space) an original form was later joined by an invader, a
stable hybrid population appeared as the aboriginal form became extinct,
and it persisted for many thousands of years before becoming extinct.  The
invading form survived the second extinction as the "fittest" survivor.  An
op-ed companion piece by Richard A. Kerr (p.1842) included comments from
two renowned paleomalacologists.  Geerat Vermeij (who is a collaborator and
natal compatriot of Gijs) was quoted: "Many people think hybrids are
short-lived ... Here they lasted a long, long time."  David Jablonski put
it thus: "The great thing is that they've [Goodfriend and Gould]  projected
the [snail] population they see now back in time, and put a number on how
stable these hybrids actually were. It's evolution on action."

Goodfriend, G. A. and S. J. Gould, 1996.  Paleontology and chronology of
two evolutionary transitions by hybridization in the Bahamian land snail
Cerion. Science 274: 1894-1897. December 13.

Harry


At 01:29 PM 3/23/2004, Gijs wrote:
>Tom,
>
>Well, the discussion was about hybridization, and not on parthenogenesis. A
>deviation into that direction is OK with me, no problem. There are mollusks
>that are parthenogenetic as written before (not only by me).
>And, sorry, but "... there have to be examples..." is not good enough for
>me. Self fertilization or self pollination is not good enough. I want two
>indviduals, male and female of a hybrid, with fertile offspring (i.e. hybrid
>x hybrid) and so on for about 10 generations. Drosophila will do, any proven
>case.

>Gijs

Harry G. Lee
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