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Re: apogamy

Wim posed this question:

why are they doing so well? Apogamous species with a Tertiary distrubution must be rather old, no (e.g. Phegopteris connectilis)?
The way I understand it, apogamy occurs when the egg cell has been too long without a sperm (ignoring the whole issue hybrids). The egg cell "gets old" and undergoes an internal duplication of its chromosome compliment to reach 2N, and then proceeds to develop as if it had been fertilized. So apogamy provides a mechanism to overcome lack of free water or very low spore numbers, but does not replace normal sexual reproduction. Perhaps the very old apogamous species are doing so well because they can reproduce in a wider range of habitats and conditions than non-apogamous species. The way I see, it, more individuals in more habitats means more opportunities for genetic variation in response to environmental change as long as apogamy is facultative, not obligate.

On Jan 7, 2005, at 6:54 AM, Winter, Wim de wrote:

Apogamy is a quicker easier more reliable way to reproduce.
Well, is that generally true? It is the solution to overcome two very
different problems:

1. it makes the gametophyte independent of free water necessary for
fertilization, thus enabling the apogamous species to reproduce in dryer
environments, helped by the somewhat faster development;

2. it bypasses the impossible meiosis in species with a genome that cannot be
divided in two equal sets of homologous chromosomes (normally hybrids that
have not polyploidised).

The cost are high: no more sex. An organism without sex is like a manager that
doesn't listen to his subordinates: though he can survive on his existing
knowledge he will not get any new ideas for business expansion or adaptation
to a changing market. Even organisms that are normally parthenogenetic ;like
bacteria go at length to exchange some body fluids now and then. The whole
idea of evolution is largely based on modification and mixing.

It is true, however, that when you're a fern growing happily at a suitable
location, you'd rather have your self multiplied than have you sprores blown
away and go all the way through the vulnerable gamo stage en fertilization.
Many ferns therefore have found that some vegetative reproduction in addition
to spores is a useful novelty to acquire.

So generally it appears to me that apogamy is no advantage, though an
emergency fix in extreme situations (unsuitable environment, wrong
chromosomes). But the question remains: why are they doing so well? Apogamous
species with a Tertiary distrubution must be rather old, no (e.g. Phegopteris


[demime 1.01d removed an attachment of type application/ms-tnef which had a name of winmail.dat]

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