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Re: apogamy

  • Subject: Re: [ferns] apogamy
  • From: Don Avery averycfn@sover.net
  • Date: Mon, 10 Jan 2005 13:39:02 -0500

Regarding apogamy, I have been sharing the emails with a knowlegable fern neighbor, Arthur Gilman, of Marshfield Vermont, who would like to contribute to the discussion.
Thank you, Don Avery

Phegopteris connectilis (s.l) is known
to have a sexual, diploid race in Japan, as well as triploid (Europe and North America),
and tetraploid (North America only) races. Both the triploid and tetraploid races

are apogamous, and their apogamy is apparently obligatory. But, recent work has shown
that the triploid - the obligate apomict that "must breed true" - is surprisingly
variable at the molecular level. [See Driscoll et al., Rhodora 2003]. There may be ways
for variability to arise and be captured by the overall genome, i.e, to be spread through
the population. For example, somatic variation would be passed through to succeeding generations.

There may be some chance for capturing of genes from the diploid as well, and this is perhaps
how the tetraploid arose - since the gametophyte of the triploid produces viable (3n) sperm
(but abortive eggs), a (3n)sperm may have fertilized a haploid (1n) egg (from the diploid race),
resulting in a tetrapoloid (4n) race. But we should also not forget that there are some instances
of even sexual fern species persisting through millions and millions of years apparently unchanged,
and the tertiary flora of the mixed mesophytic forest is well known as a very stable assemblage.

The apomictic life style may be a 'dead end' but that end may be very far off indeed, with all
sorts of possibilities - chromosome doubling to restore sexuality, for example - in between. Rather
than a 'dead end' it might be better to think of these apomicts as 'placeholders'.

Art Gilman

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