Regional dissociated heterochrony in multivariate analysis.

Area of Science:

• Evolutionary Biology
• Developmental Biology
• Geometric Morphometrics

Background:

• Heterochrony traditionally uses a univariate concept of shape, limiting its application to multivariate data.
• Multivariate shape data analysis, while visually similar to bivariate allometry, requires new terminology beyond classic heterochrony.
• Understanding evolutionary changes in developmental timing requires robust analytical frameworks.

Purpose of the Study:

• To investigate the limitations of classic heterochrony in multivariate shape analysis.
• To explore the relationship between multivariate shape, size, and developmental trajectories.
• To adapt heterochrony concepts for modern geometric morphometric approaches.

Main Methods:

• Simulated idealized multivariate ontogenetic trajectories to analyze behavior in principal component plots.
• Applied geometric morphometrics to adult and subadult crania of Pan paniscus and P. troglodytes.
• Digitized 47 landmarks and 144 semilandmarks on neurocranial surfaces to capture detailed shape data.

Main Results:

• Classic heterochrony terminology is insufficient for describing complex multivariate shape changes during development.
• "Dissociation" in heterochrony is algebraically equivalent to regional dissociation, varying by anatomical region.
• Species' growth trajectories must align perfectly in shape space for classic heterochrony to apply simply.
• The growth trajectories of Pan paniscus and P. troglodytes are too complex for global heterochrony summaries.

Conclusions:

• Multivariate geometric morphometrics reveals complexities in evolutionary developmental patterns that classic heterochrony cannot fully capture.
• New analytical approaches are needed to understand heterochrony in the context of complex, multivariate shape evolution.
• The study highlights the limitations of univariate frameworks in modern evolutionary and developmental biology research.