Dietary quality and encephalization in platyrrhine primates

Area of Science:

• Evolutionary biology
• Primate evolution
• Comparative anatomy

Background:

• High energetic costs of brain development may limit encephalization.
• The expensive-tissue hypothesis (ETH) posits gastrointestinal tract reduction facilitated primate brain expansion.
• Diet quality is proposed as a key factor in overcoming metabolic constraints on brain size.

Purpose of the Study:

• To investigate the relationship between diet quality and encephalization in platyrrhine primates.
• To test the predictions of the expensive-tissue hypothesis within a diverse primate clade.
• To determine if diet quality explains variations in relative brain size among platyrrhines.

Main Methods:

• Phylogenetic comparative analysis of diet quality, endocranial volume, and body size in platyrrhines.
• Statistical control for phylogenetic effects to isolate diet-brain size correlations.
• Examination of specific taxa (e.g., Brachyteles) and dietary reconstructions of ancestral platyrrhines.

Main Results:

• A significant phylogenetic signal was detected for diet quality, endocranial volume, and body size.
• After controlling for phylogeny, no significant correlation was found between relative diet quality and relative endocranial volume.
• The platyrrhine primate Brachyteles exhibits a large brain size despite a low-quality diet, contradicting ETH predictions.

Conclusions:

• Diet quality does not appear to account for the observed differences in encephalization among platyrrhine primates.
• The findings suggest that a shift in diet quality was unlikely the primary factor enabling increased encephalization in platyrrhines.
• Extrapolation to humans indicates that diet quality may not be the sole or primary driver of human brain evolution.