I've read in several places (can get references if necessary) that oaks
( Quercus spp.) hybridize very easily. If so, wouldn't - over
millennia - speciation be lost and all oaks blend to a single
homogeneous oak? If hybridization is so easy - what keeps the species
apart? How does tell if a particular "wierd" specimen is a hybrid or a
new species? Am I expecting botany to be too exact?

If DNA analysis was extremely inexpensive (say, $ .10) would botanical
taxonomy be void of ambiguity?

In message .com,
Raphanus writes
I've read in several places (can get references if necessary) that oaks
( Quercus spp.) hybridize very easily. If so, wouldn't - over
millennia - speciation be lost and all oaks blend to a single
homogeneous oak? If hybridization is so easy - what keeps the species
apart? How does tell if a particular "wierd" specimen is a hybrid or a
new species? Am I expecting botany to be too exact?

There are other processes which may operate to limit introgression.
Apart from selection against hybrids such processes include hybrid
sterility and hybrid breakdown.

I don't know much about oaks, except that hybridisation is widespread
within the oak subgenera, but I can give you examples from another
genus.

Hybrid sterility - the hybrid between Malva sylvestris and Malva durieui
is fairly easy to produce. However it is triploid and highly sterile,
with a seed set of under 1%. The germination rate is also low - from
circa 200 seeds I only managed to raise 2 plants this year.

Hybrid breakdown - the hybrid between Malva sylvestris and Malva linnaei
is also fairly easy to produce, and has appreciable seed set (~ 5-10%).
Germination is again poor - from circa 100 seeds I raised 8 plants. But
these plants appear to highly sterile.


If DNA analysis was extremely inexpensive (say, $ .10) would botanical
taxonomy be void of ambiguity?


No, unless you can find a convenient locus. Gene trees are not perfectly
correlated with species trees, and closely related species may not be
separated absolutely by DNA sequences. Examples that come to mind - from
ornithology - are the Larus argentatus (herring gull) and Loxia
curvirostra (crossbill) complexes.

Introgression and hybrid speciation also complicate matters.
--
Stewart Robert Hinsley

Stewart Robert Hinsley wrote:
In message .com,

...such processes include hybrid
sterility and hybrid breakdown.

Thanks. I think I understand the above. Now that I think about it,
this sort of had to be answer. The "mule" problem. I'm sure this is
Botany 101 and I appreciate you taking the time to give me a lesson.


No, unless you can find a convenient locus. Gene trees are not perfectly
correlated with species trees, and closely related species may not be
separated absolutely by DNA sequences.

I get some of this - but not all. I'll make a stab at asking a further
question. If closely related species are not separately absolutely by
DNA sequences - what are they separated by? I thought that with
respect to speciation DNA determined everything. E.g., the genome of
the Neanderthal and the genome of the human are different. I'm sure my
ignorance and confusion is showing. Could I be using "DNA analysis"
when I mean "genome determination?" Thanks in advance.

Just to make the discussion more surreal---many, many interspecific
hybrids among plants are fully fertile. That old "fertile offspring"
rule pretty much has to be thrown out the window when working with the
plant world.

Monique Reed.

In message . com,
Raphanus writes

Stewart Robert Hinsley wrote:
In message .com,

...such processes include hybrid
sterility and hybrid breakdown.

Thanks. I think I understand the above. Now that I think about it,
this sort of had to be answer. The "mule" problem. I'm sure this is
Botany 101 and I appreciate you taking the time to give me a lesson.


No, unless you can find a convenient locus. Gene trees are not perfectly
correlated with species trees, and closely related species may not be
separated absolutely by DNA sequences.

I get some of this - but not all. I'll make a stab at asking a further
question. If closely related species are not separately absolutely by
DNA sequences - what are they separated by? I thought that with
respect to speciation DNA determined everything. E.g., the genome of
the Neanderthal and the genome of the human are different. I'm sure my
ignorance and confusion is showing. Could I be using "DNA analysis"
when I mean "genome determination?" Thanks in advance.


Only a few loci may be involved in speciation. In the Loxia curvirostra
complex (crossbills), speciation is associated with changes in beak
shape and size (adaptation to feeding on different types of conifer
seed) and calls (species identificiation). Speciation is so recent that
at other loci, including those typically used for studying phylogenies,
show pretty much the same variation in each species.

For a botanical example, ITS/ETS doesn't seem to fully resolve Sidalcea.

If you look at the whole genome then I'd guess that phylogenies would be
pretty much unambiguous, at least at the level of flowering plants. But
there'd still be the problem in identifying which populations represent
species.

Mimulus cupriphilus is restricted to the workings of a couple of
Californian copper mines. It appears to be a recent derivative of
Mimulus guttatus (IIR the parent species C). On a phylogeny, for most
loci, it's probably nested within M. guttatus, and just by looking at
the DNA sequence you couldn't tell it was a new species - you'd also
need to be able to predict the phenotype from the genome.

For another example of a potential pitfall, the populations of Gossypium
aridum found in one Mexican state have had their chloroplasts and about
3% of nuclear loci replaced by those from a relatively distantly related
species from Baja California. If you'd looked only at the cpDNA you'd
have drawn the wrong conclusions about the taxonomic affinities of those
populations.
--
Stewart Robert Hinsley

Thanks. You've given me a very good feeling about the situation - and
food for further study.


Stewart Robert Hinsley wrote:
In message . com,
Raphanus writes

Stewart Robert Hinsley wrote:
In message .com,

...such processes include hybrid
sterility and hybrid breakdown.

Thanks. I think I understand the above. Now that I think about it,
this sort of had to be answer. The "mule" problem. I'm sure this is
Botany 101 and I appreciate you taking the time to give me a lesson.


No, unless you can find a convenient locus. Gene trees are not perfectly
correlated with species trees, and closely related species may not be
separated absolutely by DNA sequences.

I get some of this - but not all. I'll make a stab at asking a further
question. If closely related species are not separately absolutely by
DNA sequences - what are they separated by? I thought that with
respect to speciation DNA determined everything. E.g., the genome of
the Neanderthal and the genome of the human are different. I'm sure my
ignorance and confusion is showing. Could I be using "DNA analysis"
when I mean "genome determination?" Thanks in advance.


Only a few loci may be involved in speciation. In the Loxia curvirostra
complex (crossbills), speciation is associated with changes in beak
shape and size (adaptation to feeding on different types of conifer
seed) and calls (species identificiation). Speciation is so recent that
at other loci, including those typically used for studying phylogenies,
show pretty much the same variation in each species.

For a botanical example, ITS/ETS doesn't seem to fully resolve Sidalcea.

If you look at the whole genome then I'd guess that phylogenies would be
pretty much unambiguous, at least at the level of flowering plants. But
there'd still be the problem in identifying which populations represent
species.

Mimulus cupriphilus is restricted to the workings of a couple of
Californian copper mines. It appears to be a recent derivative of
Mimulus guttatus (IIR the parent species C). On a phylogeny, for most
loci, it's probably nested within M. guttatus, and just by looking at
the DNA sequence you couldn't tell it was a new species - you'd also
need to be able to predict the phenotype from the genome.

For another example of a potential pitfall, the populations of Gossypium
aridum found in one Mexican state have had their chloroplasts and about
3% of nuclear loci replaced by those from a relatively distantly related
species from Baja California. If you'd looked only at the cpDNA you'd
have drawn the wrong conclusions about the taxonomic affinities of those
populations.
--
Stewart Robert Hinsley