-------- Original Message --------
Subject: Re: Phylogenetic size correction with sexual dimorphism
Date: Fri, 11 Nov 2011 18:00:00 -0500
From: Mauricio Torres <[email protected]>
To: [email protected]
Dear Emma,
you can quantify, for each species, the intersexual difference in each
relative warp for the average-size hypothetical individual. That
difference can be estimated with methods similar to those used to
produce a typical thin-plate spline. The idea is that if you compare the
average male vs the average female using thin-plate splines, a species
with little sexual dimorphism will show little deformation, and one with
a high level of dimorphism will have a deformed grid. The magnitude of
deformation can be estimated and used as an indicator of sexual
dimorphism. Such measurement of sexual dimorphism for each RW can be
analyzed with PGLS, using size as one of your predictor variables.
Best wishes,
Mauricio
=================================
Mauricio Torres-Mejia
PhD Candidate
Department of Biology
University of California, Riverside, CA, 92521
USA
http://student.ucr.edu/~rtorr006/
2011/11/11 morphmet <[email protected]
<mailto:[email protected]>>
-------- Original Message --------
Subject: Re: Phylogenetic size correction with sexual dimorphism
Date: Fri, 11 Nov 2011 15:01:56 -0500
From: Dean Adams <[email protected] <mailto:[email protected]>>
To: [email protected] <mailto:[email protected]>
<[email protected] <mailto:[email protected]>>
Emma,
Adding very short branches to the tips of your phylogeny for males and
females in each species won't necessarily cause the phylogenetic VCV
matrix to be singular, just as having polytomies won't necessarily
cause
this matrix to be singular. In fact, adding very short branches was one
early way (albeit clunky) in which within-species variation was
included
in PGLS analyses; prior to Felsenstein 2008 and other more recent
approaches (see e.g., Ruber and Adams 2001: J Evol. Biol.).
So you might give this approach a try for your project.
Best,
Dean
--
Dr. Dean C. Adams
Associate Professor
Department of Ecology, Evolution, and Organismal Biology
Department of Statistics
Iowa State University
Ames, Iowa
50011
www.public.iastate.edu/~__dcadams/
<http://www.public.iastate.edu/~dcadams/>
phone: 515-294-3834 <tel:515-294-3834>
On 11/11/2011 1:53 PM, morphmet wrote:
-------- Original Message --------
Subject: Phylogenetic size correction with sexual dimorphism
Date: Fri, 11 Nov 2011 14:26:10 -0500
From: Emma Sherratt<emma.sherratt@gmail.__com
<mailto:[email protected]>>
To: [email protected] <mailto:[email protected]>
Dear fellow morphmetricians,
I am stuck on the methods for phylogenetic size correction in my
study
looking at sexual shape dimorphism across a number of species.
I have size and shape data for 50 species, averaged for males
and for
females in each species. The averages have been made from measuring
several individuals per sex per species. So data structure is n
= 100
(50 males, 50 females).
I want to correct my shape data for size, taking into account
phylogenetic non-independence, so that the phylogenetic
size-corrected
data in the original format, i.e. for each species an average
for males
and average for females. This is because I want to examine the
sexual
shape dimorphism in a PCA morphospace.
Normally to correct for size in geo morphometric shape data, I
would use
a multivariate regression (a la Monteiro 1999 Sys Biol) and
take the
residuals for subsequent analyses.
For correcting for evolutionary allometry, I would take the average
shape and size for each species, and run a multivariate
regression using
either independent contrasts or make a phylogenetic VCV matrix
from the
tree.
Where I run into a problem is that for each species, I have
data for
both sexes, and since I want to study the dimorphism between
sexes, I
cannot simply use an average for species during the regression.
It doesn't work to have zero length branches for males and
females in
the phylogeny, since this leads to extra independent contrasts, or
singular values in a VCV phylo matrix.
Any ideas?
Regards,
Emma
---
Emma Sherratt, PhD.
Post-Doctoral Fellow in Organismic and Evolutionary Biology
and Museum of Comparative Zoology
Harvard University
26 Oxford St.
Cambridge, MA 02138
[email protected]
<mailto:[email protected]><__mailto:emmasherratt@fas.__harvard.edu
<mailto:[email protected]>>
