Assessment of modularity in the urodele skull: an exploratory analysis using ossification sequence data.

Area of Science:

• Developmental biology
• Evolutionary biology
• Comparative anatomy

Background:

• Understanding developmental modules is crucial for evolutionary developmental biology.
• Urodele skulls offer a model for studying cranial ossification patterns.

Purpose of the Study:

• To investigate the presence and nature of developmental modules in urodele skulls.
• To evaluate the efficacy of different statistical methods for identifying modularity.

Main Methods:

• Principal Component Analysis (PCA) on ossification sequences.
• Phylogenetic Independent Contrasts (PIC) to assess correlations.
• False Discovery Rate correction for multiple testing.
• Binomial tests, cluster analysis, and Evolutionary PCA.

Main Results:

• PCA suggested up to four modules, but PIC identified only two significant modules.
• Two bones showed no clear association with identified modules.
• Phylogenetic signal was detected, but homoplasy was pervasive.
• Canonical variates analysis differentiated neotenic urodeles.

Conclusions:

• Phylogeny-informed methods like PIC are more reliable than PCA for studying developmental modularity.
• Urodele cranial ossification exhibits significant modularity.
• Cranial ossification patterns may distinguish neotenic species.