Re: Nest predation

[John Bois <jbois@umd5.umd.edu>]

On Fri, 5 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 had thought that parental care was more reliable because of extant
phylogenetic bracketing (since crocs and birds do it nonavians did it
too). Because you couldn't bracket with nest parasitism it would seem a
less useful trait.

> 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?  

Don't you mean "...one that is lost and gained many times or one that is
*lost* and gained a handful of times."  

Yes, the first makes more noise but if you make the assumption that the
second is therefore more reliable, you are more likely to listen more
carefully to it, thus effectively amplifying it!

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

Right.  Except that they are all under construction.

> >I think my difficulty with the particular trait under discussion is that
> >it seems rather obviously ephemeral...and being ephemeral (if it
> >is) we can move to adaptationist hypotheses such as: given certain
> >preexisting conditions trait X is likely to evolve at some frequency.
> 
> ***only within the crown group.***

No.  I mean universally.  This could be true for Hymenoptera or
Archosauria or any group that has developed the following
preconditions: host species has large investment in parental care; host
cannot discriminate parasite; parasite has higher reproductive success
parasitizing than immediate ancestor had not parasitizing; species are
both oviparous.
But then systematics only deal with the states of existence and not how
they got to be that way.  But while cladistics can inform hypotheses of
origination (for example, my hypothesis of parental investment being
selected to increase embryonic rate depended upon phylogenetic
relationships between archosaria, birds, crocs, and dinos), I suspect the
reverse is not true.  Adaptationist hypotheses cannot and should not be
used to construct phylogenies.
Chris, I suppose it's obvious that I am fairly ungrounded in this
discussion.  I appreciate your teacherly attitude.  I have purchased
_Encyclopedia of the Dinosaurs_ and am dragging my way through a
discussion of systematics.