Date: Thu, 4 Sep 1997 09:16:57 From: SCHLAUER@chemie.uni-wuerzburg.de To: cp@opus.hpl.hp.com Message-Id: <aabcdefg3358$foo@default> Subject: Re: Hybrids and fertility
Dear Derek,
> I keep hearing/reading about various CP hybrid species not being fertile
> either self- or cross-.
This is *NOT TRUE* for all hybrids. In fact, within the limits of
cps, only comparatively few cases of sterile hybrids in the genus
_Drosera_ are known (cf. e.g. the masses of repeated crosses or
hybrids involving no less than six different parent species in the
genus _Nepenthes_).
> I'm not sure I understand why?
There is no good explanation to a wrong hypothesis.
> For one thing,
> I thought (obiously wrongly) that species were only fertile to the same
> species, so I guess I don't understand how hybrids can be developed
> anyway.
Forget this wrong hypothesis ASAP! We are talking about *PLANTS*. The
interspecific sterility hypothesis only applies to *ANIMALS* (and not
even to all of them!), and perhaps a few other nasty creatures.
Zoologists tend to extrapolate everything they have discovered in
(sometimes only one single species of) animals to all living things,
ignoring that plants are quite fundamentally different in many
respects. Some Botanists tend to believe everything they read or are
told by Zoologists, and rather cite that than to make an experiment
or examine the literature more thoroughly.
My tip: simply don't believe anything and only trust what you
actually see. Very much is written and told, and only a part of it is
true.
> I've always been under the impression that a "hybrid" was a
> cross between two differing _variations_ in a distinct species.
Definitely not *only* within a species (v.s.).
> So, if you can cross
> differing species, then, since you have a "valid" genetic combination,
> why does it seem that so many of them are sterile? I would expect that
> any valid genetic combination should be able to reproduce.
Wrong conclusion because of wrong premise (v.s.). NB: There are
several different definitions of the term "valid". In the ICBN,
"valid" means a name that has been established according to the rules.
This does not tell anything about the fertility of the respective
plant. Therefore, you should maintain the terms "sterile/fertile" and
not "valid" here.
> And I suppose, along similar lines, since Nepenthes are male/female
> differentiated, does it make any difference to your hybrid which sex of
> which species you're crossing? (i.e. is a Male mirabilis x Female
> gracilis the same thing as a Female mirabilis x Male gracilis? I'm just
> pulling species names that I can think of, I don't know if that's even a
> valid cross...) Or is there no difference at the genetic level, but the
> common naming is different to differentiate the two?
There is definitely a difference at genetic level. Apart from
(generally) 1/2 of the chromosomes in the nucleus, all intracellular
compartments, incl. mitochondria and plastids and their respective
DNA are inherited from the mother (female parent) plant. But there is
no formal difference in the scientific *naming* of the hybrid
(parents in alphabetical order). In order to reflect the (sometimes
observable) differences between the different crosses,
horticulturists frequently write bastard formulae with the female
parent first.
> Of course, there's that whole thing with horses and
> donkeys that I never understood either...
This is one of the exceptions alluded to above. Sometimes exceptions
are quite illustrative for the general rule, sometimes they are just
confusing...
My modified general rule for hybrid fertility (and some other
phenomena): General rules do generally not apply. ;-)
Kind regards
Jan
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