Evaluation of Shape Complexity Metrics
Our first task was to assess what component of shape was driving
increased complexity scores across the dataset. We define ‘complexity’
as the difference between the 4th and
20th harmonic model. On average across all taxa, the
4th harmonic model describes 87.9% of the complexity
of the original femur shape and 85.5% in the tibia, while the
20th harmonic model describes around 99.7% of the
complexity of the original segment shape both segments. Thus, gross
complexity comprises approximately 14% of the total shape complexity.
On a qualitative level, the main visual difference between the
4th and the 20th harmonic outlines
appears to be the presence of large spines in the 20thharmonic outline. This would suggest that gross complexity is heavily
influenced by these ‘major’ spines. Indeed, initial inspection of
boxplots suggests that species that are characterised by larger spines
relative to the central pedipalp shaft have high gross complexity scores
(see Figure 2). Observationally, the total number of large spines also
appears to influence gross complexity. This is best illustrated in the
tibial segment, in which species with relatively long but few large
spines, such as H.longicornis and P.whitei , have lower
gross complexity scores than other species with a larger number of
‘major’ spines. The tibia segment was found to have a statically higher
complexity (Wilcoxon, p = <0.001, v = 2849) than the femur.