Galapagos Iuridae scorpion outlier

John Grehan jrg13 at PSU.EDU
Wed Apr 17 20:56:56 CDT 2002


At 12:10 PM 4/18/02 +1100, you wrote:
>This is a 'matters arising' for John Grehan. I'm curious as to the rationale
>behind his treatment of a taxon, and hopefully it will be of wider
>interest to a
>few others. JG's Galapagos paper shows a group of scorpions, the Iuridae,
>distributed along the Western side of the Americas. There are  also
>apparently some in the Mediterranean. He links the two groups westwards
>across the Pacific and Asia, I guess some 200 degrees of longitude roughly
>(fig.10 - particularly eyecatching), when a minimum spanning link would be
>100  degrees or so eastwards across the Atlantic. Why John?  I realise this
>link is presented in the discussion, not the results, is more in the
>nature of a
>speculation, and the alternative is indeed mentioned (but not figured), but
>isn't this a violation of the fundamental minimum distance panbiogeographic
>technique?
>
>Geoff

No. The minimum spanning link is the simplest choice  in the absence of
other information such as phylogenetic relationships and main massings.
Main massings are an important consideration in delineating baselines and
this is explicitly stated in a number of panbiogeographic publications.
However, I would agree that I did not describe this aspect adequately in
the methods section of the paper. In the case of the Iuridae the main
massing is western America. The western massing and the Mediterranean
occurrence conform to a classic Pacific pattern so it is my speculation
that the distribution may represent a highly disjunct Pacific distribution.
Of course it is possible that the western massing of the Iuridae in the
Americas is an artifact of extinctions in eastern North and South America
as well as Central America, and western Africa and Europe. In my opinion
the available spatial evidence shows more support for a Pacific rather than
Atlantic origin.

>Also the Med outlier is not mentioned when earlier the Iuridae
>appear as an example of East Pacific tracks in the results.  Maybe the
>criteria for degree of relatedness comes in to play here, but there's no
>background given on that.  What's the story here?

The Mediterranean occurrence was not a necessary component for describing
the East Pacific track, but for examining the origin of the East Pacific
track it was included to examine the intercontinental relationships of the
American distribution.

Of course I fully accept that all my choices in track construction and
interpretation are open to critique, and others may come up with a better
supported panbiogeographic alternative.

John Grehan




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