Centre of origin digression

[Robin Leech]

Don,
Yes, they do contain historical evidences, but because they
cannot be measured under a microscope, or cannot be processed
in the normal way through molecular systems, they are usually
deleted as being viable.  It takes a bigger mind to use them.
Robin

----- Original Message -----
From: <Don.Colless at CSIRO.AU>
To: <TAXACOM at LISTSERV.NHM.KU.EDU>
Sent: Monday, April 04, 2005 11:54 PM
Subject: Re: Centre of origin digression


John and all:

As I suspected, the mosquito subgenus seems to have been tidied away by
recent  workers. The bibionid (Enicoscolus) remains. By "make no sense
geographically" I should perhaps have written "make little sense prima
facie". I'm aware of other trans-Pacific distributions, but that doesn't
stop me from wondering how such things might have occurred. They cry out for
EXPLANATION. It's not enough to draw "tracks" on the map; what are they
tracks OF? Obviously a story could be cooked up to explain any track at all;
but what we need (if possible!)are ones that gain credibility by fitting
other available evidence - the way "Antarctic" distributions fitted so well
with continental drift. Of course Wegeners are pretty thin on the ground;
but let's keep our eyes out.

I don't know about "geographic artefacts", but surely distributions contain
historical evidence.


Don Colless,
Div of Entomology, CSIRO,
GPO Box 1700,
Canberra. 2601.
Email: don.colless at csiro.au
Tuz li munz est miens envirun



-----Original Message-----
From:   Taxacom Discussion List on behalf of John Grehan
Sent:   Mon 4/4/2005 11:10 PM
To:     TAXACOM at LISTSERV.NHM.KU.EDU
Cc:
Subject:             Re: Centre of origin digressionDon Colless,


Blimey, Don puts up a challenge too hard to resist! I don't know about
'explaining' a distribution, but one might wonder about Croizat's slogan
"dispersal forever repeats'. The question that one might first ask about
the examples given by Don is whether they are 'exceptional' in some way,
or run of the mill. To Don the distributions 'make no sense
geographically' This is a common kind of refrain in biogeography - that
people working with particular groups cannot make sense of their
geography and it seems that this problem arises from not being aware of
the geography of life in general or in having an adequate geographic
framework for comparing distributions.

We draw attention to this in our 1999 book were we draw attention to
examples (p. 67) such as Jeffrey (1988) noting the "astonishing
geographical disjunction" of Dactyliandra welwitschii between SW Africa
and India, or the astonishment of Touw (1993) in finding a continental
Asian moss on Madagascar. We point out that such disjunctions (centers
of astonishment) are remarkable only for their lack of geographic
continuity, and so it goes for the Norway-New Zealand disjunction
mentioned by Don. As a connection, however, this pattern is entirely
normal and run of the mill - common enough to be boring. There are many
distribution connections (tracks), for example, between various parts of
Europe and New Zealand that track, to a greater or lesser extent, the
Tethyan geosyncline. Perhaps the Norway-New Zealand disjunction is just
a subset distribution of a very common and boring biogeographic
relationship. One might, for example, see the mosquito subgenus as an
element of the connection shown by the admiral butterfly distribution
that also includes Norway and New Zealand.

As for the bibionid fly in north Queensland and New Guinea with several
others in central America (I would be grateful for the citation), it is
a perfectly good example of a central trans-Pacific track. There are
innumerable examples in the literature. Although different in geographic
detail, the bibionid biogeography is replicated in the distribution of
Playroptilon (Matile 1990) present in Queensland and New Guinea as well
as South East Asia, and Central-Northern South America. Similarly, the
distribution of dibamid snakes disjunct between South East Asia and
eastern Mexico is different in geographic detail, but has the same
biogeographic orientation.

Geographic disjunctions are geographic artifacts that can overwhelm the
individual systematist if they are not aware of geographic patterns in
general. It is this generality of biogeography that is usually missing
in the quest for centers of origin holy grail.

John Grehan



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