Centre of origin digression

[Karl Magnacca]

On 4 Apr 2005 at 17:16, Robert Mesibov wrote:
> "To give an example, in a book on the crickets of Hawaii, a population from
> the island of Molokai was separated specifically from identical ones on Maui
> because "all species in this genus are island endemics".
>
> This is taking the idea to an extreme, and using location as the _only_
> diagnostic character for the species. On the other hand, knowing how insects
> love to baffle taxonomists with cryptic speciation, those geography-based
> cricket names could be seen as "placeholders" for genetics-based cricket
> names in the near future.

Perhaps; although given the rest of the book I don't think there was
that much forethought (I admit that was an extreme example).

> I work with poorly vagile, terrestrial animals which typically form
> allopatric/parapatric mosaics of closely related forms. If field work shows
> that there are, indeed, parapatric or narrow-gap allopatric boundaries
> between forms (i.e., after convincing myself that two differing forms from
> distant locations don't grade into one another in the intervening country),
> I name each form as a species.

I'm not sure I understand this; does it mean that you find what you call
a single species in discontiguous patches of habitat, intermixed with
others, or that each patch in the mosaic is a separate species?  And how
do you differentiate "forms" reliably, if there isn't enough
morphological distinction to separate them as species without
geographical considerations?

> These I see as "evolutionary species" in the
> Wileyian sense. They've differentiated from a common ancestor and in my
> judgment are unlikely to fuse again in reticulation. Sometimes there's very
> little morphological variation within a mosaic tile, sometimes a fair bit.
> I'm thus using geographic AND morphological information to delimit species.

I can understand that (though I also wonder what makes it so unlikely
that they'll come back together, and how you distinguish between
variation within and between a tile).  I think you have a fairly unusual
situation though, and I don't think it takes very much mobility to keep
up a scenario of interchange between the tiles rather than what's
happening with yours..

> The spatial patterning smells more of history, and I'm strongly
> tempted to think (as A.R. Wallace did 150 years ago) that forms which are
> both morphologically and geographically isolated arose earlier (and are
> survivors of a clade which is now largely extinct) and that forms which are
> morphologically and geographically closer arose later.

There are indeed lots of those; but there are also lots of cases of a
large, relatively homogeneous group of species with strange offshoots in
isolated areas.

> But I'm told there isn't any phylogenetic evidence in distribution
> information. What I need to do is win a lottery and pay for a thorough
> genetic study of a wide taxonomic and geographic range of individuals. This
> will give me an inherent-character phylogeny to compare with the one I've
> roughed out from my irresponsible and indefensible use of geographical
> information (and some morphological clues, but these are few and tainted
> with suspected homoplasy).

How did you do the geographical phylogeny?  By taking adjacent or
parapatric species as being most closely related?

Karl
=====================
Karl Magnacca, USGS-BRD
PO Box 11, Hawaii Natl. Park, HI 96718
"Democracy used to be a good thing, but now it has
gotten into the wrong hands."   --Sen. Jesse Helms