Thanks for your reply. I've only been on-line for a short while and from
your discussion it appeared decidedly Lamarckian.
In regards to climate - how were climates so different in the past in
Australia and South America? Both continents have drifted north after
separation from Antarctica and you already stipulated that similar climates
exist on both continents. But climate differences aside, how could climate
influence rates of mutation within a Drosera (or any organism)? If I
follow your argument right you say that Drosera are evolving at a faster
rate on Australia than in the rest of the world. How? I would think that
the rate of mutation would be constant at the genus level. And if they
aren't - why not? So if random mutations within a genus is normalized then
that leaves only mutations generated by external forces (i.e.. radiation).
I would think that radiation while possible varying through time would not
vary much by locations. An exception to this are the north and south poles
which are subjects to greater levels of radiation. But then South America
is closer to Antarctica (and the south pole) so that doesn't seem to help
your argument.
You also mention that "These mutations were certainly very numerous..."
Why? I believe, as indicated above, that mutations occur at a steady rate
in both Australia and South America. As for rate I have no idea. Now you
have to realize that mutations are taking place on a plant by plant basis
(not on the genus as a whole). If a mutation happens that allows a single
plant to reproduce better (evolve), and for it offspring to reproduce
better (evolve) then it will dominate an environments in a relatively short
period of time (in a matter of years or decades). You would not expect
mutations to occur in any order between any two plants so you shouldn't
expect to see the same adaptations in multiple areas. There is no reason
why the same mutations that produced tuberous Drosera in Australia couldn't
produce tuberous Drosera in South America. BUT the chance of this
mutations happening in the same order and would be astounding (but I think
we agree on this point). In regards to water stress - your argument makes
a lot of sense.
Finally in regards to the origin of Drosera. I did not misunderstand you
saying a larger number of Drosera taxa could mean that's where the genus
originated. If you stick to the "could" then its true. There is also a
equal chance that it "could" have evolved in South America, or Antarctica,
or Africa. The number of extant taxa only indicates recent speciation, not
the ancestry of the genus. A question put forward by Magnus Thor'n that
the highest genetic variance in a genera occurs in the area where it
originated has been taken for fact and it isn't necessarily so, especially
for a genus that evolved such a long time ago and has radiated around the
world. I think you can argue that Drosera evolved in the southern
hemisphere because its most "primitive" taxa occur there [New Zealand,
South Africa, and South Africa fide Jan Schlauer (31 May re. specs x gens
(long!)]. But all the southern continents were connected when Drosera
evolved and I don't think you'll be able to tell exactly where it came
from.
Best regards
Chuck