[Taxacom] Hypothesis: How Nothofagus rafted to New Zealand

[Ken Kinman]

Dear All,
     Now back to dispersal (sorry for the rant against panbiogeographers who 
overdo the vicariance thing, but Grehan really provoked me this time and was 
asking for it in my opinion; I'm tired of being called a Darwinian 
dispersalist when I recognize lots of vicariance too).   Anyway, I got to 
thinking about the additional evidence that Nothofagus menziesii of New 
Zealand sharing the same species of fungi (Cyttaria gunni) with Nothofagus 
cunninghamii of Tasmania and adjacent Australia.  Not surprising since they 
are very closely related members of subgenus Lophozonia.

     My hypothesis is that one (or more) Nothofagus cunninghamii trees 
rafted to New Zealand carrying on their branchs both their own fruit and 
their unique fungus Cyttaria gunni.  The tree or trees could have been 
dislodged due to land slides, massive floods, or even a tsunami---pick your 
favorite disaster.

    Nothofagus can float for very long distances, even ALL the way from 
Chile to Tasmania (see Barber, 1959, in the journal Nature; "Transport of 
Driftwood from South America to Tasmania").  Therefore, floating the shorter 
distance from Tasmania to New Zealand would have been comparatively easy, 
especially in some of the strongest ocean currents in the world.

     Some of the fruits would have been held above the ocean surface, so the 
salt water couldn't ruin them, and fruits that might not have been fully 
ripe yet would have provided further protection to the seeds inside.  In New 
Zealand, the new population evolved into a new species (N. menziesii) due to 
the founder effect.  The Cyttaria gunnii fungi apparently didn't speciate 
(or maybe it actually has and it just hasn't been shown yet by molecular 
testing).  But can't rule out Cyttaria getting to New Zealand at a later 
time independently.

     The same rafting mechanism could have taken Nothofagus gunnii to New 
Zealand to found the truncata-fusca-solandri group (all four form a clade in 
subgenus Fuscospora).  Or maybe a bird could have done this as well, since 
these species apparently have no Cyttaria fungi associated with them 
(although one could perhaps even imagine a bird eating both Nothofagus 
cunninghamii seeds and Cyttaria spores before taking off for--or being blown 
to--New Zealand).  Next I need to look into mosses and insects which may be 
(like Cyttaria) unique to Nothofagus.  No telling what all a floating tree 
could have carried over with it, and I need all the evidence I can in order 
to get Grehan off my back.  But enough for one day.  I'm tired.
      ----Cheers,
            Ken Kinman

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