Allometry and phylogenetic divergence: Correspondence or incongruence?

Area of Science:

• Evolutionary biology
• Primate morphology
• Geometric morphometrics

Background:

• The relationship between within-species variation (e.g., allometric change) and phylogenetic divergence is a long-standing question in evolutionary biology.
• Understanding size-related shape changes in craniofacial proportions is key to primate evolution.

Purpose of the Study:

• To investigate if the direction of static allometries in craniofacial proportions diverges with increasing phylogenetic differences in Old World monkeys.
• To assess the impact of sample size and taxonomic sampling on the analysis of allometric divergence.

Main Methods:

• Utilized geometric morphometrics on a large sample (>3200 specimens, 51 species) of adult Old World monkeys.
• Analyzed static allometries of craniofacial proportions and their divergence in relation to phylogenetic differences.
• Conducted sensitivity analyses and randomized subsampling experiments to evaluate the effects of sampling error.

Main Results:

• Static allometries in craniofacial proportions varied broadly in direction, showing no discernible phylogenetic signal.
• Variation in static allometries was greater than previously observed in ontogenetic trajectories of Old World monkeys.
• Sampling error was found to contribute to inaccuracies, magnifying differences in allometric change.

Conclusions:

• There is no congruence between static allometric divergence and phylogenetic divergence in Old World monkey craniofacial morphology.
• Accurate morphometric research requires very large and representative samples to mitigate sampling error.
• Allometric variation may not be a reliable indicator of phylogenetic relationships, but the study of size-related shape changes is vital for understanding morphological evolution.