Date: Fri, 28 Apr 2000 11:15:03 -0400 From: "PHILIP SHERIDAN" <psher001@odu.edu> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg1329$foo@default> Subject: Re: Pitcher plant inbreeding
Hi Folks:
In answer to the question on pitcher plant inbreeding we have an answer.
Our article on this subject has been accepted by the American Journal of
Botany and should be out sometime in the fall. We did a five year study
of all the S. flava populations in Virginia and found that they are
extremely inbred. We looked at selfing, crossing within a site, and
outcrossing to different sites. We measured seed number, seed mass,
avg. seed mass, germination, survivorship, and growth. In other words
we assessed the fitness as a result of the treatments. Results? The
selection against selfing is 92% (and this is before we even get to
flowering stage!). What this says then is that if S. flava is
self-pollinated in Virginia the chances of it making it to maturity and
reproducing are basically nil. In terms of your propagated plants with
S. flava DON"T SELF. Yes you will get some seed but it is very probable
that in all aspects of physiology they will not be as robust as
outcrossed seed. What our data suggests is that S. flav a has a high
genetic load (many mutations) which result in decresed fitness upon
selfing (because you end up with recessive alleles in a homoxygous state
where they can be expressed).
Now, the outcrossed picture (pitcher?) is more complicated. We found
that crossing with pollen from all sites produced the greatest fitness
compared to crossing within a site (crossing all sites was 26% better
than crossing within a site). However, if you only cross between two
sites you may get some outbreeding depression as a consequence of local
adaptation. These classical genetic studies basically support the
electrophoretic work of Godt and Hamrick at UGA.
Now, can you take the results of S. flava in Virginia and apply them to
other pitcher plants? In the case of S. flava throughout its range and
the related S. oreophila I think the answer is yes (for a number of
reasons I won't go into here). However, be very cautious with other
Sarracenia species. We have completed similar work with S. purpurea and
are working on a paper on that species. At this point it looks like
some Sarracenia species carry a lower genetic load (e.g S. purpurea and
S. rubra) and selfing can result in high seed yields with excellent
fitness. This makes sense, especially with S. rubra, since the flowers
can self-pollinate (and we have experimental evidence to back this up)
and deleterious alleles may have been purged long ago.
A long story here and I could keep going with a lot of the nuances but
you will have to invite me as a speaker for that! Hope this helps.
Sincerely,
Phil Sheridan
Director
Meadowview Biological
Research Station
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