Comparing morphotypes

Authors
Affiliation

Floriane Remy

CNRS, Univ. Bordeaux, MCC – UMR 5199 PACEA

Frédéric Santos

CNRS, Univ. Bordeaux, MCC – UMR 5199 PACEA

Once the inter-individual variability has been described, and the factors explaining it highlighted, it can be useful to represent this morphological variation. To do so, the mean shape (also called morphotype or consensus) of each group of interest may be plotted together, so they could be compared.

Depending on the nature of the available data (2D or 3D), these morphological differences can either be represented as vectors, through a thin-plate spline or a surface color map.

1 Visualizing the differences between two configurations

The R function geomorph::plotRefToTarget() can be used to visualize the shape differences between two different landmarks configurations (as already illustrated in another section). For instance, Figure 1 shows the differences between the global mean shape of the sample, and one given individual.

## Global mean shape:
Mglob <- mshape(gpa$coords)

## Shape differences with the first individual:
plotRefToTarget(Mglob, gpa$coords[, , 1], method = "TPS")
mtext("TPS")
Figure 1: Shape differences between the first individual and the global mean shape.

2 Comparing the morphotypes of various groups

The previous function can thus be used to compare the mean shapes of several groups, for instance the mean shapes of females and males.

The following code allows for the computation of female and male morphotypes respectively.

## Compute female and males morphotypes respectively.
Mfemales <- mshape(gpa$coords[ , , meta$Sex == "F"])
Mmales <- mshape(gpa$coords[ , , meta$Sex == "M"])
Exercise
  1. Use the function geomorph::plotRefToTarget() to compare the mean shapes of females and males. What can you say about the amount of sexual dimorphism?
  2. Which limits can you see for this approach? How to fix them?

Hint for the R code:

plotRefToTarget(Mfemales, Mmales, method = "TPS")
mtext("TPS")
Figure 2: Shape differences between female and male morphotypes.
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