No subject

[Arisaema Enthusiast Group (AEG) Discussion List (and other=]

hardy  Aroids)" <ARISAEMA-L at NIC.SURFNET.NL> Aroids)" <ARISAEMA-L at NIC.SURFNET.NL>
Sender: "Arisaema Enthusiast Group (AEG) Discussion List (and other=
From: Susanne Renner <Renner at UMSL.EDU>
Subject: evolution of sex change doesn't require inbreeding depressi=
on 
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

Dear David,

Yes, obviously arisaemas do things one way, while others plants d=o
things another way.

Selfing followed by inbreeding depression does not strike me as t=he
most plausible selective factor behind the evolution of sex change/gender
choice in Arisaema.  The flowering plants that change sex (mainly Arisaem=a,
Gurania, Psiguria, Catasetum, Cycnoches, Mormodes, Elaeis, Panax, a few
Acer) all possess strong temporal separation between male and female
function in the closest relatives of the sex-changers.   It therefore is
unlikely that the ancestors of the sex-changers suffered from self
pollination and inbreeding depression.  Rather, I suspect, that the
selective factor for the evolution of sex change may lie in extreme
environmental heterogeneity from one year to the next.   (This is known a=s
the patchy environment hypothesis for the evolution of sex change.)  An
alternative model is what's know as the size advantage hypothesis.  This
hypothesis holds that an invidual should start out as the sex that suffer=s
the least pentaltity from smallness (normally this is the male sex) and
then switch to the sex that reaps the biggest benefit from size (normally
this is the female sex as it takes more resource to mature seeds than mak=e
pollen).  Both models explain sex change without resorting to inbreeding
depression.

Susanne