[Taxacom] An improved definition of cladogenesis

[Curtis Clark]

On 3/13/2010 7:48 AM, Kenneth Kinman wrote:

>              I think we are getting down to heart
> of the problem. We all seem to be in agreement that cladogensis can only
> be observed in retrospect. HOWEVER, due to the fuzziness of species
> boundaries, we cannot say that the pregnant female (or even her
> offspring) are where "cladogenesis" occurred. They could have still
> easily have potentially interbred with the original mainland
> individuals, and are therefore still just an isolated SUBspecies.  If
> the female got to the island, some of her offspring could get back to
> the mainland (even easier if we aren't talking just about islands).

A totally unnecessary complication in this specific example. Remember we 
are looking in retrospect. None of those things happened.

>              I think Richard is just pointing out
> that "cladogenesis" cannot usually be pinned down to any particular
> generation of individuals.

Yes, but not for the reasons you give (or even necessarily the ones he 
does). Vicariance speciation can in fact be "fuzzy", and we should not 
spin our wheels looking for fuzziness when it doesn't exist at the 
expense of studying it where it does.

> Generation 10 may be incapable of
> interbreeding with the original mainland population, but individuals of
> generations 3 through 8 could have easily been able to interbreed with
> both the original mother species and the new daughter species.

It doesn't matter a bit whether they could, if they didn't. Conflating 
cladogenesis and anagenesis simply makes both terms less useful.

>            It's this fuzziness of species boundaries
> that makes it impossible to pin down where "cladogenesis" occurred.

I guess I haven't been communicating well. If I'm reading you correctly, 
you want species boundaries to be by default fuzzy, but there are plenty 
that (again in retrospect) are quite sharp. Ignore that at your peril. :-)

> Thus
> cladogenesis is just a special series of anagenetic events that
> occasionally result in a new species. That's why I argue that there is
> rarely a clearcut distinction between cladogenesis and anagenesis.

I utterly and totally reject that view. Cladogenesis and anagenesis are 
about pattern, not process. By conflating them, you rob both terms of 
any usefulness.

>                The only case where there is
> arguably a clearcut distinction is the sudden origin of a polyploid
> species from a diploid mother species. However, although you can call it
> cladogenesis, you can just as easily look at it as rapid anagenesis.

IF your only tool is a hammer, everything looks like a nail. Ken, 
reducing everything to anagenesis isn't a requirement for recognizing 
paraphyletic higher taxa.

>         Therefore, I offer for your consideration a more concise (and
> less confusing) definition of cladogenesis.  "Cladogenesis is a series
> of anagenetic events which results in a new species."

I find that this has no use. It simply seems like a way to deprecate 
"cladogenesis" in favor of "anagenesis".

> P.S. I guess that is why we argue so much over species concepts,
> especially in cases where the speciation process may be incomplete. Are
> we at generation 100 yet? Or is it still at generation 60 where they
> could get sucked back into the mother species given certain future
> environmental changes (historical contingencies).  I guess that is why I
> feel a phylogenetic species concept can result in oversplitting, and
> subspecies being labelled species prematurely.

Unless I have misconstrued your background, we (specifically) argue over 
species concepts because I have studied speciation in a number of 
specific groups (which may or may not be typical, but they span the 
sorts of speciation documented for angiosperms), and you haven't. My 
views are informed by my experience.

-- 
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Director, I&IT Web Development                   +1 909 979 6371
University Web Coordinator, Cal Poly Pomona