----- Original Message -----
From: "Marco Oliverio" <[log in to unmask]>
Subject: Re: Poecilogony: pairs of species
> well,
> the debates is actually interesting! Maybe a little too technical to some.
> Anyway, may I add my two cents. What am I used to do when I meet two
shells
> with different protoconch and nearly identical teleoconch? ...the answer
at
> the end of this message.
>
> The science of interpreting and understanding the evolution of larval
> development still lacks a crucial info: the genetics controlling these
> features of the development. We don't know wheter there is a single gene
> for the planktotrophy, or a cluster of coordinated genes, or even
> independet genes operating to produce the extended velum, the cilia, the
> feeding mouth etc...
> And what about the egg production? What gene(s) is(are) operating to
> produce a planktotrophic embryo? And is just a matter of maternal effect?
I
> mean, the gene(s) of the mother determine the kind of egg (planktotrophic
> vs. lecithotrophic), then the fate of the daugther larva is already
> determined in the genes of the mother... ?? In turn what about her sons.
> And finally (??) what about the influence of the environment? Can the
> environmental parameters influence the direction of development?
> The accumulated experience on the pairs suggest that two populations with
> different development very likely represent two distinct species under the
> biological species concept. But the sole indication that they develop in a
> different way is NOT a definitive proof. It simply indicate that they have
> some different biological properties, NOT hat they are two distinct and
> isolated gene pools.
Marco,
in fact, the moment a planktotrophic species (P) produces a lecithotrophic
(L) or direct developing "daughter" species, the gene pools are expressed
differently, but that of the daughter species is also more restricted (lots
of genes drop out, because by chance they are not present in the mother
specimen[s]). Maybe in some cases the overlap in prevents the daughter
species to become fully detached, but nevertheless this is the onset of the
drifting apart of the L daughter gene pool, especially if the daughter lives
quite isolated from the P mother species (say, as isolated as Darwin's
finches are from the South American continent).
Most cases (but they're very very few!!) so far
> examined by independent tools (allozyme, DNA) seem to indicate different
> species. I have diagnosed by allozymes Columbella rustica (Mediterranean,
> lecithotrophic L) from Columbella adansoni (Atlantic, planktotrophic P)
> otherwise indistinguishable (except protoconch of course).
You may argue that additional evidence in the form of differences in DNA and
(or?) allozymes is necessary to establish an L daughter as a bona fide
species, however my point is that if you accept the P/L switch as crucial,
then there is no place for the concept op poecilogony. In other words, it is
just a matter of definition, and I believe the one proposed by me is not
only the most parsimonious, but also a workable hypothesis in the sense that
it can be proved or falsified. The concept of poecilogeny on the other hand
cannot.
> OLIVERIO M., 1995. Larval development and allozyme variation in the East
> Atlantic Columbella (Gastropoda: Prosobranchia: Columbellidae). Scientia
> Marina, 52(1):77-86.
> But I have failed attempting to separate by the same markers Rissoa
> auriscalpium (P) from Rissoa italiensis (L) and R. rhodensis (L), and
> Rissoa violacea (P) from Rissoa sp. (L), either in allopatry or in
sympatry.
I simply believe that the P/L split in these taxa is (much) more recent than
that in Columbella.
> OLIVERIO M., 1994. Developmental vs. genetic variation in two rissoid
> gastropod complexes. Journal of Molluscan Studies, 60: 461-465.
> At this regard a colleague tells me he has some indication from finer DNA
> markers (SNIPS) that the two sympatric populations of Rissoa from the Gulf
> of Naples (auriscalpiumP/italiensisL) are diagnosed (hope he publishes
> soon!!).
>
> I have summarized my ideas in:
> OLIVERIO M., 1996. Contrasting developmental strategies and speciation in
> N.E. prosobranchs: a preliminary analysis. In (J.D. Taylor ed.) Origin and
> evolutionary radiation of the Mollusca. Chpt. 22, pp. 261-266. Oxford
> University Press.
> OLIVERIO M., 1996. Life-histories, speciation and biodiversity in
> Mediterranean prosobranchs gastropods. Vie et Mileu, 46(2): 163-169.
>
> And the global scale of the phenomenon and its relevance in recently
> modelling the patterns of biodiversity in:
>
> OLIVERIO M., 1997. Global biodiversity and life-history evolution in
> prosobranchs gastropods. Iberus, 16: 73-79.
>
> My personal position and practice as concerns taxonomy is the following: I
> use different names for populations of caenogastropods with different
> development (thus protoconch). It is - in my opinion - the most
> conservative position, I would say the most parsimonious. Admitting
> poecilogony, giving the present knoledge (still scarce) would require to
> hold assumptions that are evolutionary more ... expensive. This is just my
> personal position, that I know is shared my many, but I can't tell if we
> are the majority ... nor if we are rigth.
We may not be right, but we're practical.
Marien
www.mollus.nl
>
> But the discussion is STILL OPEN: Nature does not like to conform to our
> rigid schemes of B/W, +/_, either/or, plankt/lecith. Often - more often
> than we realize - the grey area is full of interesting critters ....
>
>
>
> =========================================================
> Marco Oliverio - Evolutionary Biology PhD
> Research Scientist
>
> Dipartimento di Biologia Animale e dell'Uomo
> Viale dell'Universita' 32
> I-00185 Roma ITALY
>
> phone +39.06.49914307
> FAX +39.06.4958259
> e-mail: [log in to unmask]
>
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