[MORPHMET] Centroid size correlation with size

[Agnese Lanzetti]

Hi all,

I am encountering a strange pattern in my data and I'm not sure if it is a 
problem with how i am collecting the landmarks or it's actually just a 
strange but correct pattern.

I work with an ontogenetic series of baleen whale skulls. The skulls of the 
fetal specimens are very small (10-30 cm in length) compared to newborns or 
adults (80-120 cm length). I would expect from my understanding of centroid 
size to increase progressively going from the early fetuses to the adults, 
but this is not the case. The fetal stages seems to overall follow the 
pattern from small to big, but newborns and adults have more variable 
centroid sizes that overlap with the range of the fetuses.

I collect my landmarks in Avizo, and I changed the scale of the 3D models I 
imported from other software to scale the skulls to their real size. 

Do you think there is a problem with the landmark collection or it could be 
possible that centroid size does not approximate actual skull size in this 
case?

Thanks a lot!
Agnese
agnese.lanze...@hotmail.it



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[MORPHMET] PLS analysis skull ontogeny MorphoJ: weird pattern observed

[Agnese Lanzetti]

Hi all,

I am getting weird results when doing a PLS analysis in MorphoJ.

I have a dataset of 12 minke whale skulls of different ontogenetic ages and I 
wanted to test if the anterior part (rostrum) and posterior part (braincase) 
are modular and how their shape changes relative to one another during growth.
Both parts are blocks of the same configuration and they are on the same 
Procrustes fit, as recommended for these kinds of studies.

I am getting strange results on the block 1 PLS1 vs block 2 PLS1 graph, with 
all the specimens falling on the same "line" (looks like a linear regression 
with a 45' slope), but instead of having the specimens ordered from the 
youngest to the oldest, with youngest close to 0 and oldest at the other end, 
the pattern is strange.
The adults fall around the middle of the distribution, with the youngest 
specimens close to 0 and intermediate specimens at the top of the distribution. 
So it kind of seems that the shapes are "reverting" back in adults compared to 
younger specimens.

Unfortunately I can't attach an image so I tried to describe the problem in the 
best way possible.
Have you ever seen a pattern as the one I described? If not, in your experience 
is it biologically possible or it implies that there is something wrong with my 
data?
I think my limited sample size might be part of the problem, but I'm not sure 
if that's the only reason why I'm seeing this pattern.

Let me know if you need additional info.
Thank you very much!
Best,
Agnese Lanzetti

agnese.lanze...@hotmail.it
Ph.D. candidate
Joint Doctoral Program in Evolutionary Biology
San Diego State University
University of California, Riverside

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