idependent evidence, was: Re: Real biogeography problem

[Thomas Schlemmermeyer]

Hello, I would like to take the comment by Dr. Hovenkamp, to stir up a little
bit the problem of independent evidence.

Allopatric distribution is independent of sister-relationship in the sense that
distribution is a spatial attribute with no, or only weak genetic base.
Sister-relationship, on the hand, is supposed to be exclusively gene-based.

Using now evidence from one field, let us say, distribution, to corrobate
evidence from another field, phylogentic relationship, is a comparatively old
procedure which has been applied by Hennig and Croizat.

But is it still valid (I think philosophically this is called "mutual
enlightening") in the light of modern epistemiology?

On (         Fri, 1 Oct 1999 09:40:14 +0200
),         "P.Hovenkamp" <Hovenkamp at NHN.LEIDENUNIV.NL> wrote:


>At 11:06 AM 30-09-99 -0700, Fred Rickson wrote:
>>Maybe a real biogeographic problem would be enjoyable and helpful to the
>>current discussion.  I would love to have some help/discussion/brainpower
>>thrown at a current biogeographic situation I am working with.so here is a
>>REAL problem.
>
>I'm afraid this kind of real problem is not going to help the discussion
>much. So far, the discussion was concerned with Earth history - that is the
>problem of reconstructing  geographical/geological events on basis of
>biotic data.
>
>The real problem thrown at us here concerns Taxon history - that is, the
>reconstruction of the history of a particular taxon.
>
>As Fred Rickson notes, on basis of a single datum (allopatry of
>sister-groups) it is not possible to distinguish a vicariant from a
>dispersal event. And we shouldn't try to.
>
>We can tentatively diagnose vicariance events on basis of repeated
>allopatric sister-group relationships (whether these are represented as
>tracks or in any other way, I don't greatly care), but we can use
>vicariance events as an explanation for the occurrence of a single
>sister-group relationship only if we have at least some independent
>evidence that these events have really happened.
>
>Peter Hovenkamp
>>
>>Humboldtia is a genus of small legume trees with 4 species distributed
>>along the Western Ghats of south India (moist areas).  Individuals are
>>quite gregarious often forming small area of 10s to 100s of trees.  Two
>>species have special morphological structures which facilitate occupation
>>by ants and other invertebrates.  Two species do not have most of these
>>special traits.  Now, a fifth ant-associated species exists in Sri Lanka
>>(same moist requirement) and forms dense little areas of many, many trees
>>(very common).  DNA analysis shows the Sri Lankan tree sister to the most
>>eastern of the Indian species, also an ant form.  On the basis of
>>morphology the Sri Lankan species is also the most advanced of the five.
>>No other species of this genus exist.
>>
>>So, it seems to me as if the south Indian area is ancestral and Sri Lanka
>>is derived.  If any of the Indian species ever occurred in Sri Lanka, or
>>vice versa, I would think the species would still be around given the
>>gregarious and successful nature of all of the species within their home
>>range.  Now, do I draw a track from the Indian sister species to Sri Lanka
>>and claim vicariance across the former, but now submerged, land bridge, or
>>do I just do the botanical thing and suggest a wanton seed sometime after
>>the Eocene became established, and subsequently evolved into the Sri Lankan
>>species?  I really don't have any idea of an answer to this distribution
>>question.
>>
>>Now that is a tight little story and there is still no easy answer.  I may
>>have some help because a proposed comparison of the invertebrates living in
>>association with each species (within swollen, hollow, self-opening stems)
>>might shed some light on whether whole plants and there pals marched across
>>the land bridge, or seed arrived and the plants have picked up a new,
>>unrelated set of friends.  Any comments appreciated, biogeographical or
>>otherwise.
>>
>>
>>Fred R. Rickson
>
>P. Hovenkamp
>Rijksherbarium, Leiden
>The Netherlands
>hovenkamp at rhbcml.leidenuniv.nl
>http://rulrhb.leidenuniv.nl/
>


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Thomas Schlemmermeyer
Museu de Zoologia, Universidade de São Paulo
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São Paulo, SP, Brasil

Residência:
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