RE: apogamy

Betty:

>As a triploid, it must have arisen through a chance hybridization between a 
>diploid and triploid species, 

More likely a diploid x tetraploid.

>Further, more such populations increases the chance that a spontaneous 
>doubling will occur, creating a fertile hexaploid, and thus the potential for a 
>successful, sexually reproducing species.   

In higher plants many triploids will show some limited fertility when pollinated by tetraploid plants. but this varys quite a bit.  In Lilium many triploids are amazingly fertile for a triploid when pollinated with pollen from a tetraploid lily.  The resulting progenies are almost always tetraploid.  

If a triploid produces an unreduced gamate it could be fertilized by a haploid gamate from a diploid and also produce a tetraploid =>  3N + 1N = 4N.

Don't know how applicable this is to ferns, but in might be possible.

>In habitats where members of the same genera occur together, hybrids between 
>parents with the same number of chromosomes are likely to be fertile.

That depends on how compatabile the two genomes are.  In genus Lilium you can cross two Asiatic lilies and often times get a fertile hybrid, but cross an Asiatic with a trumpet liliy or a trumpet lily with an Oriental lily or Easter lily with Asiatics, for example (using embryo rescue), and the progenies are infertile although all lilium species are 2N=24.  On the pther hand, I'm working with some hybrids between species with vary different chromosome numbers, 2N=22 and 2N=28, where you would think the resulting progenies would be completely infertile and yet the hybrids will produce a few seedlings, although the level of fertility is about 0.01% of normal.  Still, IF you make enough crosses you can recover that rare seed.  Given the number of plants that may exist in any breeding population, even a very low probability will still occure from time to time.

Joe Halinar

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