-------- Original Message --------
Subject: Re: Analyzing ontogenetic trajectory angles
Date: Tue, 19 Jul 2011 13:42:00 -0400
From: [email protected]
To: [email protected]
Dear David,
Im writing a R package (named "ontogeny") with a
colleague (Giancarlo Ferrara) containing functions
used in
Paolo Piras, Paolo Colangelo, Dean C Adams, Angela
Buscalioni, Jorge Cubo, Tassos Kotsakis, Carlo Meloro
and Pasquale Raia. 2010. The Gavialis-Tomistoma
debate: the contribution of skull ontogenetic
allometry and growth trajectories to the study of
crocodylian relationships.Evolution and Development
12(6):568-79
These new functions are newely developed functions
(albeit inspired by Dean Adams past papers and Piras
et al 2010)
You are refrerring in your post to the ontogenetic
convergence test of our paper. This can be applied to
any linear model (not only, of course, to ontogenetic
data)
Let me know if you (or everyone else) need the
function code. I cand send it to you.
-------- Original Message --------
Subject: Analyzing ontogenetic trajectory angles
Date: Mon, 18 Jul 2011 14:46:19 -0400
From: David Katz <[email protected]>
To: [email protected]
Hello,
I have read several morphometrics papers which test
for significant
differences in ontogenetic trajectory between two
groups (species,
subspecies, etc) by calculating the "angle" between
their growth
trajectories. However, parts of (or even lots of) the
method remain
unclear to me.
First, it seems that calculation of the angle requires
calculation of
two simple regression lines, one for each group, with
the angle being
the arc subtended by the two lines. One axis for
these regression
plots/calculations is the distribution of specimens
along a PC which is
significantly correlated with size or age (usually the
first PC). But
it is not clear to me what the second axis is. Log
centroid size?
Second, the significance of the angle is tested by
randomly permuting
specimens between the two groups 1000 or more times,
then calculating a
new angle for each permutation. Significance is then
tested against the
distribution of permutation-generated angles. But
what is the
permutation procedure? Do we only permute a single
specimen each time?
Third, if I'm understanding the method correctly, then
absent an
additional scaling step, the two lines from which the
angle is
calculated are not likely to be of the same length.
How is this
accounted for, if at all?
Any help, or a reference to a good, explicit journal
or book
explanation, would be very much appreciated.
Thanks.
David Katz
Doctoral Candidate
Department of Anthropology--Evolutionary Wing
University of California, Davis
Young Hall 204
/--Trying to focus on one distraction at a time/--
