Hybridization   Robert Leverett
  Feb 01, 2005 06:04 PST 

Lee:

   This brings up the whole subject of hybridization. In terms of those
you see in the upper Mid-west, in your judgment, which ones are the
most ecologically significant - if that is a sensible question. I guess
I am wondering which hybridizations create special habitat value,
enhance species survivability, species competitiveness, etc. Are the
seeds of the hybrids as viable as those of their parents? Lots of
babble. I guess I'm just fishing for a better general understanding of
the hybridization process and what it portends, at least for certain
species. I'd venture to bet that there are a lot of us on the list who
have many more questions than answers about the significance of natural
hybridization.

Bob
RE: Hybridization   Lee E. Frelich
  Feb 01, 2005 06:35 PST 

Bob:

Some hybrids are superior competitors or are uniquely adapted to certain
habitats where the parent species don't do well and come to dominate there.

If the hybrid is fertile, then this is a mechanism by which new species can
arise.

Just as often, however, the hybrids are not any better adapted than either
species, but there are lots of them, and they persist anyway. Black, red
and northern pin oaks on sandy soils in Wisconsin are a good example.
Rarely can I tell what species these trees are, but they cover a few
million acres in central Wisconsin, in a semi-dwarf to moderately statured
forest with trees 10-50 feet tall. The prominent forest ecologist Grant
Cottam told the students in his ecology class (including me) that if you
can throw a stone and hit a jack pine, then the oak tree you are standing
near can be called pin oak, otherwise it is a black oak. I would add that
if you are not on sandy soil and you can throw a stone and hit a sugar
maple, then its a red oak, otherwise its a black oak. These rules just give
you something to write down on your tally sheet. Who knows what the real
species is, if the species concept applies at all.

On sandy loam soils in northern Wisconsin we also have yellow birch-paper
birch hybrids mixed in with hemlock. These trees can be seen at Plum Lake
Natural Area. They have the bark of paper birch and the leaves of yellow
birch. Red maple and sugar maple also hybridize, producing red maples with
leaves shaped like sugar maples, and sugar maples with red maple
bark. These maple and birch hybrids are not very common--it must be
difficult for pollen of one species to successfully fertilize the other
species, and/or most of the hybrids are not fertile and don't persist.

Lee
RE: Hybridization   edward coyle
  Feb 01, 2005 07:12 PST 

Bob,

In my North American Trees book by Preston & Braham, it lists only one
hybrid and intergrade for white ash, and that is Texas ash. Green ash has
none. However in his listing for Pumpkin Ash (Fraxinus profunda), he states
that" based upon the number of chromosomes, some authorities think that
pumpkin ash developed from hybridization between white and green ash."
It is found from SE Va. To central Fla., SW Ind. to S Tenn. With several
disjunct populations even to Ohio and Indiana. It is associated with
lowland, floodplain species.

In that same book it lists hybrids for oaks, many of them, for almost
every species. So many in fact, that if even half were fertile, we will not
be able to separate them eventually.
That 'Mule Oak" (phellos x pagoda), from the Congaree trip is a recent
example. My wife suggested the name after I told her I didn't know if it was
fertile.

Ed C
RE: Hybridization   Robert Leverett
  Feb 01, 2005 07:45 PST 

Ed:

Thanks. Interesting material. A question that comes to mind is whether
or not there a hierarchy among species in terms of inclinations to
hybridize. I am under the impression that red and black oaks hybridize
at the drop of an acorn, but that red and sugar maples do it rarely.
Lee's explanation in the last e-mails certainly suggest that. I wonder
what role stress plays. How readily do various species of hickories
hybridize? Again, I wonder if there is a discernable hierarchy.

   I was also interested in Lee's observation about field work in terms
of the frequency of hybridizations and the relative infrequency of
scientists to venture into the field to collect data. The old warm
laboratory versus inclement weather choice?

Bob
RE: Hybridization   edward coyle
  Feb 01, 2005 08:11 PST 

Bob,

Briefly, the Pecan hickories (Apocarya), and true hickories (Eucarya) both
hybridize, each with the other.

Don't leave out the white oaks, they hybridize like there was no tomorrow.
As for silver x red maple cross, he suggests it occurs readily when the red
is the female parent.


Ed C
RE: Hybridization   Gary A. Beluzo
  Feb 01, 2005 08:33 PST 

Lee:

Interesting. Your post has piqued my interest. Given the fact that the
"species" concept really lies along a continuum, what criteria in plants
(say trees specifically) are used to determine whether or not two similar
organisms are to be considered in the same species or not? In other words,
how genetically distinct must two trees be in order for most botanists to
consider them separate species? Does the degree of hybridization (observable
by phenotype) suggest actual cladistics?

For those of us that don't have access to DNA analysis and related tools,
are there some good rules of thumb for observing degree of speciation in the
field?

Gary
RE: Hybridization    Will Blozan
   Feb 02, 2005 19:18 PST 

Do you know the name for the Acer rubrum x saccharinum hybrid?
RE: Acer rubrum x saccharinum    Paul Jost
   Feb 02, 2005 20:09 PST 

It is Freeman's Maple

PJ