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hardy  Aroids)" <ARISAEMA-L at NIC.SURFNET.NL> Aroids)" <ARISAEMA-L at NIC.SURFNET.NL>
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From: "P.Bruggeman" <pbruggeman at WISH.NET>
Subject: Re: Arisaema sexual strategies; selfing A. tortuosum
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Susan,

>>Everybody who agrees that nutrition plays a big role in whether an
arisaema becomes female, and this has been demonstrated experimentally by
several workers, starting with Atkinson in 1898. You say that because of
this nutrition-depency, you don't think sex change is an important
diagnostic tool. I wasn't thinking of sexual strategy as a taxonomic
character though, but am interested in its evolution.

OK, I have misunderstood you then. Because you introduced catagories base=d
on the way some species change sex, I thought you were trying to introduc=e
some sort of classification. What I was merely trying to say was that,
because of the nutrition-dependency of the sex-change, it must be very
difficult to study this in great detail for every species and get reliabl=e
results. It is my personal believe it must be possible to get every
paradioecious species change sex without going through a bisexual stage s=o
in my opinion only the end-result counts. It would however be interesting=to
know whether a paradioecious species that goes through a bisexual stage, =is
able to self-pollinate too or that only (some) true bisexual species are
capable of this.

>>What is difficult to understand is why a plant would switch off male
sexual function when it is genetically capable of producing male gametes.
Giving up female function makes sense when you're nutrionally stressed. B=ut
male function is cheap, so why give it up once you're big and healthy? Se=x
change requires the evolution of a system that allows an ariseama to asse=ss
its nutritional status and then produce female and/or male gametes
accordingly. Why are all Arisaema capable of doing this but no other aroi=d,
not even arisaema's closest relatives?

Maybe it is because of the very same ability to self-pollinate that some
species still seem to have?. Producing only male/female flowers is the be=st
way to ensure that self-pollination does not occur. In that respect, it
would be interesting to know why A. flavum ssp. tibeticum still is able t=o
produce strictly male plants when mature (or was that a wrong observation=by
Murata?). There are indications that the other 2 ssp. of flavum evolved f=rom
ssp. tibeticum and flavum is generally regarded as one of the most primit=ive
species so maybe flavum ssp. tibeticum is the most primitive of all the
Arisaema? It is too bad nature doesn't always let species evolve to more
attractive plants because ssp. tibeticum is definitely the best looking o=f
the 3 ssp..

Pascal