-------- Original Message -------- Subject: [Fwd: Re: Morphometrics of small, variable specimens--embryos] Date: Tue, 29 Mar 2011 11:57:24 -0400 From: [email protected] To: [email protected] ---------------------------- Original Message ---------------------------- Subject: Re: Morphometrics of small, variable specimens--embryos From: "P. David Polly" <[email protected]> Date: Tue, March 29, 2011 9:42 am To: [email protected] -------------------------------------------------------------------------- Hi Eric, I think you're on the right track with mounting the same specimen more than once. If you do every specimen two or three times you can partition out the shape variation due to mis-alignment of the plane. To do this you add an additional level to your ANOVA so that it has factors for between group, between individual, and between mount variation. There are several papers you can cite for this method, but my favourite is Baily and Byrnes, 1990. A new, old method for assessing measurement error in both univariate and multivariate morphometric studies. Syst. Zool. 39: 124-130. Best wishes, David ----------------------- Dr. P. David Polly Department of Geological Sciences Indiana University 1001 E. 10th Street Bloomington, IN 47405 USA [email protected] +1 812 855 7994 http://mypage.iu.edu/~pdpolly/ (Adjunct in Biology and Anthropology) ----- Original Message ----- From: "morphmet" <[email protected]> To: "morphmet" <[email protected]> Sent: Tuesday, March 29, 2011 11:36 AM Subject: Morphometrics of small, variable specimens--embryos
-------- Original Message -------- Subject: Morphometrics of small, variable specimens--embryos Date: Tue, 29 Mar 2011 10:28:14 -0400 From: [email protected] To: [email protected] Hello all, I am currently doing 2D and 3D analyses of midgestational mouse embryos. My sample is variable owing to ontogenetic variation. Genetic variation is very minimal, as my strains are mostly congenics, having practically identical genetic backgrounds but differing only at one or two loci. The specimens are also very small. First, for the 2D analysis, I am photographing freshly harvested and unfixed embryos in three different orientations (top, lateral, and "frontal" = palatal view), mounting in a petri dish of cold saline and photo'ing two separate times per view. Each set of images per specimen is landmarked twice, and all the data will be subject to an initial procrustes ANOVA to assess the relative strengths of the different effects of mounting, landmarking, genotype, and specimen. However, I expect, and experience shows, that a significant portion of the variance in the data will be due to mounting errors. The embryos are small and difficult to position. GPA will take care of rotational errors. But slight rotations out of the plane (pitch and yaw) will produce variation in the data that will look like shape variation. My hope is that by mounting and photo'ing twice, I will reduce pitch/yaw errors. Will the mean square of the mounting effect reflect the amount of those types of errors? If I can identify a PC that appears to capture pitch or yaw, can I regress the procrustes coordinates on that PC in order to remove those errors from the data? Thanks. Eric [email protected] University of Calgary Faculty of Medicine
