Centroid size as a proxy for body size

[mariekev...@gmail.com]

Hi everyone,

I have a general question: it is generally accepted in geometric morphometrics to use centroid size of a bone as a proxy for body size. Body size is not always available, but working with centroid size can also be a bit of an overstatement. It depends on the bone or feature in question, but I can't seem to find studies that describe these disadvantages (or suggest other methods).

I worked with carpal bones of different primates, for example large silverback gorillas and small slender gibbons. Mightworking with centroid size have some effect on the results?

Are there other ways to take body size into account? Or take into account that centroid size is not always ideal to work with?

Thanks!

Marie.

[Donald Swiderski]

Marie,

There is, of course, an enormous literature outside of geometric morphometrics on the relationship of various dimensions of limb bones to body mass and the ways those relationships change as a function of body mass and behavior (including locomotion). I’m guessing from your post that you already know that literature and are anticipating that the relationship of body size to centroid size will depend on what dimensions of the bone are captured by your landmarks. I would add that in the case of those carpal bones, the relationship of an individual carpal to body mass will also depend on whether that bone’s contribution to total carpal cross-section area varies across the sample.

In other words, I think it is up to the individual researcher to determine whether the centroid size of a given set of landmarks is a good proxy for body size, or whether a different measurement, perhaps independent of the landmarks used to study shape, is a better proxy for body size.

If it should be the case that some measurement other than centroid size is a better predictor of body size (in your case, maybe the cross-sectional area of the radius), you would simply replace centroid size with that measurement in your analysis of the allometric relationship.

Don

Donald L Swiderski
University of Michigan
ph.(734) 846-6208
e-mail: dlsw...@umich.edu

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[Adams, Dean [EEOB]]

Marie,

 

This is really a question about scaling of relative parts, not so much a question regarding centroid size.  If the bone in question scales isometrically with body size, then estimates of that bone can be used as a proxy for estimates in overall size. However, we know that most components of an organism grow allometrically, so that will be a challenge.

 

While centroid size is used as a size measure in many studies, the interpretation is usually restricted to that body part: either CSize of the overall body or of the part.

 

It may be a bit of an overstatement to measure a particular bone and extrapolate that it represents the body size scaling of the set of organisms under study.

 

Dean

 

Dr. Dean C. Adams (he/him)

Distinguished Professor of Evolutionary Biology

Department of Ecology, Evolution, and Organismal Biology

Iowa State University

https://faculty.sites.iastate.edu/dcadams/

phone: 515-294-3834

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