Yes, applying phylogenetic independent contrasts to morphometric
data is a logical thing to do if you know that the observations
in your samples are not independent but are expected to be
correlated due to phylogeny. Partial warp scores can be treated
like any other multivariate data (with all the same potential
problems of outliers etc.). However, it does not make sense to
apply the independent contrasts method to relative warp scores.
An analysis of relative warps is just a principal components
analysis. If your observations are not independent then that
needs to be taken into account when you perform the PCA itself
not afterwards. I plan to add that as an option to my tpsRelw
software but I have not yet done that.
Comparative studies often over interpret the results. You may
wish to look at my recent paper: Rohlf, F. J. 2006. A comment on
"phylogenetic correction". Evolution. 60:1509-1515.
----------------------------------------------
F. James Rohlf, Distinguished Professor
Dept. Ecology & Evolution, Stony Brook University
Stony Brook, NY 11794-5245
http://life.bio.sunysb.edu/ee/rohlf
-----Original Message-----
From: morphmet [mailto:[EMAIL PROTECTED]
Sent: Friday, September 01, 2006 1:05 PM
To: [email protected]
Subject: Phylogenetic independent contrasts
Dear morphometricians,
my name is Carlo Meloro and I am conducting a study on the
evolution of mandible shape in large carnivores. I am
wondering if you could give me some suggestions on the use of
phylogenetic indepedent contrasts in order to validate
correlation between log transformed Centroid Size (as
independent variable) and Shape variables (that in my case
are represented by the relative warps scores). Could it be
possible to apply such a method on relative warp scores or
not? I have never seen such analysis (on relative warp
scores) before in bibliography and every title relevant to
the subject is welcome. On a preliminary analyses (in my
data) the association -tested with simple linear regression
through the origin- between independent contrasts (IC) of
centroid size and IC of relative warp score (RWs) is
significant only for the second and the third RWs. With a
simple linear regression (non-corrected for phylogeny)
centroid size is positively associated with the first and the
second relative warp scores -not the third-. These resuls are
quite contradictory.
What do you think? Any comments also on alternative method?
Many thanks in advance to your help
Carlo Meloro
Carlo Meloro
Phd student in Earth Science
Dipartimento di Scienze della Terra
Università degli studi di Napoli "Federico II"
L.go San Marcellino 10
80138, Napoli, Italy
phone: ++39 0812538331
e-mail: [EMAIL PROTECTED]
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