[Taxacom] "Masteria mystery" solved?

[Michael Heads]

Hi Ken,
 
I'm not quite sure that I follow your line of reasoning. Are you suggesting a center of origin for Masteria in Antarctica? Platnick (AMNH spider website) does not accept that the Indian species of Ischnothele belongs in the genus (America/India would be a very unusual distribution). He lists Euagrus from Taiwan, Guatemala to USA (standard trans-tropical Pacific) and South Africa (standard trans-Atlantic). The Atlantic opened about the same time that the central Pacific plateaus formed (mid-Cretaceous), which suggests a simple global process for Euagrus. 
 
I don't think Masteria is (currently) an island-hopper - all the species in the Caribbean and all but one in the Pacific are endemic to single archipelagos, compatible with allopatric differentiation in a phase of immobilism. On the other hand, its Cretaceous ancestors may well have been actively dispersing when they colonized the new areas of land provided by the plateaus (possibly from prior islands in the region).  
You suggest Mesozoic vicariance for Masteria and I agree. The large igneous plateaus in the central Pacific have drifted long distances westward (Ontong Java plateau etc.) and eastward (Inca plateau etc.). They included forest (or at least trees) and presumably there were also animals there, so... what happened to them? Could they have been incorporated into America along with the plateaus? This might explain the distinctive distribution of Masteria in America (only in the Caribbean), and in the west Pacific (west only to New Guinea - Philippines).  

Michael

Wellington, New Zealand.


My papers on biogeography: http://tiny.cc/HeadsPubs
My new book 'Molecular Panbiogeography of the Tropics': http://tiny.cc/MolPanbio



________________________________
 From: Kenneth Kinman <kennethkinman at webtv.net>
To: taxacom at mailman.nhm.ku.edu 
Sent: Tuesday, 10 January 2012 3:53 AM
Subject: [Taxacom] "Masteria mystery" solved?
 
Hi Michael,            
        I think I've solved a lot of the mystery surrounding the
Masteria disjunction.  And thankfully, I didn't need either
panbiogeography or terranes floating long distances east and west across
the Pacific.  

       I looked beyond subfamily Masteriinae to other subfamilies of
Dipluridae, and the distribution of Ischnothele jumped out at me
(neotropics plus one species in India).  Euagrus is somewhat similar,
but involved South Africa instead of India.  

       This pretty clearly points to vicariance (during the Mesozoic)
centered far to the south (in the area of Antarctica), and of course any
intermediate species still in the southern polar region would have
eventually gone extinct (from the cold in particular).  

      So subsequent dispersal of Masteria (by rafting, ballooning, or
whatever) would have been over shorter distances, perhaps the longest
being east to Fiji.  This genus is clearly a fairly good island-hopper
(in both the Pacific and Caribbean).  On the other hand, genus
Ischnothele didn't need to island-hop, but simply rode on India as it
travelled north to Asia.  

     Therefore, I predict that Masteria will be found on other islands
in the Pacific, perhaps even Borneo.  However, diplurid spiders seem to
have had little luck invading very much of Eurasia beyond the area
around India, so competitive exclusion by other mygalomorphs could be a
factor (perhaps even in Borneo). 
            --------Ken Kinman  



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