Re: Nest predation

[chris brochu <cbrochu@fmppr.fmnh.org>]

>On Thu, 4 Jun 1998, chris brochu wrote:
>
>> I would be far more
>> concerned if it showed up in hundreds of putatively unrelated species.
>> (Many thanks to the individual who corrected me on anseriform parasitism,
>> by the way.)
>
>Then the trait of parental care, since it shows up many species from
>ants to humans is more problematic than nest parasitism?

Perhaps, depending on the scale you're looking at.  It also depends on the
question you're asking.  At the level of Animalia, parental care might very
well be a problematic character state, as you describe.  At the level of
Amniota, it's not as bothersome. You appear to be making qualitative
judgements about some of these characters - i.e. parental care is somehow
more reliable than parasitism - when such judgements are unwarranted in
most instances.

>I don't see how the trait showing up in _few_ putatively unrelated species
>is more diagnostic than its presence in many.

First, a clarification - "diagnostic" has a specific connotation in modern
systematics.  It relates to the derived character states for a particular
clade.  As such, the number of times a feature evolves means nothing at all
for how diagnostic it is for particular clades.

Second - which is likelier to result in phylogenetic noise during a
cladistic analysis, one that is lost and gained many times or one that is
gained a handful of times?  This one can be tested numerically.  There are
lots of simulation studies out there that ask whether higher rates of
evolution - the conditions likely to result in some sort of convergence,
albeit at a molecular level - will confound parsimony, max like, or
distance analyses.




>
>> Without a phylogeny, how would you know that nest parasitism is ephemeral?
>
>But we've already constructed phylogenies based upon traits we have great
>confidence in.

For birds?  You're sure about that?  Have a look at the recent molecular
systematics of birds volume edited by Mindell for a different view - a few
nodes appear to be robust, but otherwise the relationships among living
lineages are very poorly resolved.  It actually looks like morphology may
be more informative than molecular data for some of these groups, and even
that has been minimally informative lately.




 Would you overturn them on the basis of the trait of nest
>parasitism?

Not at all, and I never said I would.  I would, however, be willing to
include that as a character in a total-evidence environment; in other
words, there is no reason a priori to not include that character in a
phylogenetic analysis.



All I'm saying is that some traits are more diagnostic than
>others.  I agree with you that some behaviors _are_ diagnostic.  I
>caution, though, that behavior is an evolutionarily maleable trait.

How do you measure evolutionary malleability, in the absence of a phylogeny?




 But I
>do understand there are degrees and degrees of maleability (I recently
>read a paper pointing out the unreliability of what has been traditionally
>regarded as a cladistic Rosetta Stone, mammal teeth).
>I think my difficulty with the particular trait under discussion is that
>it seems rather obviously ephemeral--but I suppose many have come a
>cropper with such famous last words as that.  And being ephemeral (if it
>is) we can move to adaptationist hypotheses such as: given certain
>preexisting conditions trait X is likly to evolve at some frequency.

***only within the crown group.***


chris






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Christopher Brochu

Postdoctoral Research Scientist
Department of Geology
Field Museum of Natural History
Lake Shore Drive at Roosevelt Road
Chicago, IL  60605  USA

phone:  312-922-9410, ext. 469
fax:  312-922-9566

cbrochu@fmppr.fmnh.org