Data from: Shape analysis of symmetric structures: quantifying variation among individuals and asymmetry

Morphometric studies often consider parts with internal left-right
symmetry, for instance, the vertebrate skull. This type of symmetry is
called object symmetry and is distinguished from matching symmetry, in
which two separate structures exist as mirror images of each other, one on
each body side. We explain a method for partitioning the total shape
variation of landmark configurations with object symmetry into components
of symmetric variation among individuals and asymmetry. This method is
based on the Procrustes superimposition of the original and a reflected
copy of each landmark configuration and is compatible with the two-factor
ANOVA model customary in studies of fluctuating asymmetry. We show a fully
multivariate framework for testing the effects in the two-factor model
with MANOVA statistics, which also applies to shapes with matching
symmetry. We apply the new methods in a small case study of pharyngeal
jaws of the Neotropical cichlid fish Amphilophus citrinellus. The analysis
revealed that the symmetric component of variation in the pharyngeal jaws
is dominated by the contrast between two alternative trophic morphs in
this species and that there is subtle but statistically significant
directional asymmetry. Finally, we provide some general recommendations
for morphometric studies of symmetric shapes.