A potential pitfall in studies of biological shape: Does size matter?

Area of Science:

• Biology
• Evolutionary Biology
• Morphology

Background:

• Geometric morphometrics (GM) is widely used across ecology, evolution, and paleontology to analyze biological shape.
• A significant portion of GM studies fail to assess or account for allometric effects, potentially leading to misinterpretations.

Purpose of the Study:

• To systematically evaluate the frequency with which published GM studies consider allometry.
• To estimate the proportion of shape variation attributable to allometric effects in the reviewed literature.

Main Methods:

• A systematic review of the 300 most recent publications utilizing geometric morphometrics for biological shape analysis.
• Assessment of whether and how allometric effects were addressed in these studies.
• Quantification of the percentage of shape variation explained by allometry when considered.

Main Results:

• 38% of reviewed GM studies did not consider the allometric component of shape variation.
• In studies that did account for allometry, it was significant in 88% of cases.
• Allometric effects explained up to 87.3% of the total shape variation in relevant studies.

Conclusions:

• Failure to account for allometry in GM analyses can lead to flawed conclusions, as size-dependent shape changes are often substantial.
• A misunderstanding of Generalized Procrustes Analysis (GPA) may contribute to overlooking allometry, as GPA removes isometric but not allometric size effects.
• Researchers are urged to evaluate the role of allometry in their specific research questions to ensure robust interpretations of biological shape variation.