Data Analysis
All data analysis was carried out in R. A principal component analysis
was conducted on all harmonic coefficients derived from the Fourier
analysis, in order to characterise intraspecific and interspecific
variation in pedipalp shape complexity. The resulting PC scores were
subject to clustering analysis in order to determine the degree to which
species may be correctly identified on the basis of Fourier outlines. PC
scores were scaled to have the same mean and standard deviation before
being fed into the clustering algorithm. An unsupervised k-means
clustering was applied; k-means was instructed to split the dataset into
11 clusters, the same as the number of species, in order to determine if
clustering would split down species lines. A pairwise MANOVA was also
conducted in ‘Momocs’.
To test the relationship between pedipalp shape complexity and length,
species-average values of ‘gross complexity’ were calculated. Due to
uncertainty in amblypgyid phylogeny, ordinary least squares regression
was then carried out between measures of complexity and pedipalp length
for each segment individually. Pedipalp tibia length is considered a
standard metric of pedipalp length and is used in multiple studies
(Weygoldt, 2000; Prendini, Weygoldt & Wheeler, 2005; McArthur et al.,
2018). As such, this was the measure of pedipalp length used herein. A
Shapiro-Wilk test confirmed that shape complexity metrics for both
segments followed a normal distribution.
Tests for sexual dimorphism in shape complexity were carried out using a
nested ANOVA between measures of complexity and sex, with species
included as a random effect. Shapiro-Wilk tests confirmed shape
complexity in both metrics was normally distributed within species, and
species standard deviations were very similar in all species.
A paired Wilcoxon rank-sum test was used to investigate differences in
shape complexity between segments, as data were non-normally
distributed. Specimens that did not appear in both the tibia and femur
dataset were excluded from this analysis, resulting in a total sample
size of 75.