Hybrids and genera

[Jeff Oliver]

I certainly lobbed one out there - I'm surprised no one swung earlier.

A couple of comments below (more like rants, so hit 'D' now if you've little
patience for the matter).

>-- Original Message --
>Date: Thu, 07 Nov 2002 11:50:40 -0800
>From: Andrew Brower <browera at science.oregonstate.edu>
>To: leps-l at lists.yale.edu
>Subject: Re: Hybrids and genera
>Reply-To: browera at science.oregonstate.edu

>Also, taxonomy could never fully "reflect phylogeny," ...

First of all, everyone agrees that the 'true phylogeny' of life is unknowable
(until that time machine gets working).  However, if we can make reasonable
estimates of that phylogeny, why should we not include that information in
taxonomy?  Most folks, scientist or not, use taxonomy as a proxy for relatedness.
 Think back to grade school - would you have ever thought birds and dinosaurs
were closely related?  No, because the taxonomy didn't reflect the relatedness.
 With very strong support for the bird+crocodilian clade, taxonomy should
reflect this, so that folks that are only exposed to High School Biology
texts, and not PNAS, could glean this knowledge.

The abandonment of phylogenetic information in taxonomy was attempted by
pheneticists decades ago, and as we all know, Cladistics came out on top
of that battle.  Although the times may be a' changin', given the arguments
between the current schools of thought (another VERY messy situation).  I'm
not making accusations about motives (the last thing I'd do was call someone
from the New York School at pheneticist), but I think we should keep in mind
the past debates about evolution and taxonomy.

>Also, taxonomy could never fully "reflect phylogeny," because if we had
access
>to the complete history of phylogeny, there would be only one taxon ("life"),
>with a bunch of polymorphic features that have changed in frequency over
>time.  

Describe terminal taxa.  Don't worry about internodes.

>The very process of conceptualizing more or less inclusive groups of organisms
>as species, genera, etc. imposes discrete boundaries among the entities
>identified, while the process of lineage splitting has no single ontological
>point at which the lineages become divided.  

I agree; that's the problem with attempting to cram a fuzzy mix of populations
into a neat typological construct for human minds.

>Kind of like, when do the Rio Negro and the Rio Solimo~es become the Amazon
>- at the point when the waters first meet, or the point where they are >completely
mixed (two very separate places)?  Are they one river, or three?  A >taxonomist
would say three, a lineage-minded person would say one.

Taxonomy (at least at the species level) is only naming a point on the river(s).
 For most points on the river (or most points in time), there are two rivers,
or there is one river.  Attempting to apply species names over long periods
of time (in which we may encounter such a coalescence) gets us into trouble.

>Taxonomy is not intended to provide an accurate map of the evolutionary
>process,

Again, if it could, why not?  Now there are hints of the Linnean hierarchy
v. Phylogenetic taxonomy in the air...

>Last, I disagree with the implication that there is an "objective biological
>definition" of species.  

So would I.  Who implied this?  Species concepts are just that: concepts.

>Given that there are multiple, competing definitions in the
>current literature, it is quite clear that the definition of species is
a
>semantic rather than an empirical or logical problem.  From my perspective,
>species are really no different than genera or families, which also "can
be >thought of as lineages" (more inclusive ones), if one desires to do so,
after >they have been recognized on the basis of fixed character state differences.
 

Definitely.

>Others probably have a different perspective.  That's the great thing about
>semantic problems.

Indeed.  I wonder how thick scientific journals would be if semantic arguments
weren't published...

>- Andy Brower, Oregon State U.
>
>Jeff Oliver wrote:
>
>> Let's not forget that 'genera' are concepts, and don't really have any
>> objective biological definition (no 'Biological Genus Concept' or >> 'Phylogenetic
Genus Concept').  'Species', despite all the different 
>> definitions given in the literature, can be thought of as lineages.  If

>> taxonomy is to reflect phylogeny, then taxa with contemporary gene flow

>> should definitely be considered congeneric, and potentially conspecific

>> (depending on levels of gene flow).  Of course, determining contemporary

>> gene flow is another ball of wax...
>>
>> Jeff Oliver
>> University of Arizona
>> jcoliver at email.arizona.edu


Jeff Oliver
University of Arizona
jcoliver at email.arizona.edu


 
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