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Re: Nest predation
>The case I am trying to make is that this particular behavior, while
>heritable, may not be appropriate for cladistical analysis; that a
>species' immediate evolutionary ecology may be a better predictor for nest
>parasitism, and that its appearance may well be somewhat independent of
>phylogenetic relationships. Rather, I should say that such relationships
>might be ephemeral.
But without a phylogenetic hypothesis, how would you know this? One might
construct the relationships among ingroup taxa without a particular feature
being scored, but if it's heritable, and therefore a potential source of
phylogenetic information, wouldn't you want to include it, since we cannot
know a priori whether a particular feature is likelier to be convergent or
In the same way that water acts as a kind of selective
>factory for making fish-shaped vertebrates, heavy parental investment may
>be a crucial prerequisite for the evolution of nest parasitism. Your
>argument above re the low frequency of parasitism in birds is a good one
>in favor of potential croc nest parasitism. But it also makes my point
>about the inapplicability of cladistics.
On the contrary, it makes it likelier that nest parasitism - provided it
is not a learned feature - will be an informative character in phylogenetic
analysis, and not a potential source of noise. 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.)
In contrast to say, bower-bird
>nesting structures, nest parasitism doesn't (I'm guessing) have a
>long pedigree within clades. (But I don't want to be misconstrued about
>cladistics. It is a valuable and illuminating tool.)
Without a phylogeny, how would you know that nest parasitism is ephemeral?
A phylogenetic analysis is the most powerful way we have to test your
hypothesis, as long is it can be calibrated.
>> >Likely rapid growth rates of dinos in vegetation mounds
>> >needed ventilation ala megapode "taking the temperature" (heat may be the
>> >stimulus for that bird's behavior. But carbon dioxide concentration is
>> >directly related to heat in these nests). Some dino nests are known to be
>> >shallow (Troodon, Oviraptor, and Maiasura).
>> So are some croc nests - not all of them build mounds of vegetation.
>Right. And a very telling point in favor of my idea that fast embyronic
>growth was a prime adaptive advantage made possible by increased parental
>investment, is the following paraphrased from Seymour and Ackerman: the
>Nile croc (ovipositing in sand) has a clutch size of about 13 kg. whereas
>the similarly-sized _C. porosus_ makes a vegetation mound but can only
>manage 5.6 kg. S & A believe this is a clutch size suppressed by lack of
>oxygen. And if _clutch size_ is restricted by limited oxygen,
>so would embryonic growth rate.
I'm not sure I agree with Seymour and Ackerman. I'll take a look at
Thorbjarnarson's more recent reviews of reproductive biology in crocs.
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