Gross intestinal morphometry and allometry in primates.

Area of Science:

• Comparative anatomy
• Primate evolution
• Gastrointestinal physiology

Background:

• Mammalian gastrointestinal tract (GIT) size is often linked to diet, with high-fiber diets expected to correlate with larger GITs.
• Statistical evidence supporting this relationship, particularly within mammal groups like primates, is limited.
• Previous assumptions about diet-GIT size correlations lack robust empirical validation.

Purpose of the Study:

• To statistically test the relationship between diet and gastrointestinal tract length in primate species.
• To investigate how body mass and dietary proxies influence the scaling of intestinal lengths.
• To examine phylogenetic influences on the diet-GIT length relationship within primates.

Main Methods:

• Compiled data on small intestine, caecum, and colon lengths for 42 primate species with known body mass.
• Analyzed scaling relationships between intestine length and body mass using phylogenetic and non-phylogenetic models.
• Incorporated dietary proxies (leaf percentage, diet quality index) as covariates in statistical models.

Main Results:

• Intestine length scaled geometrically with body mass, with exponents including 0.33.
• Strepsirrhini primates had notably long caeca, while Catarrhini had shorter ones.
• Dietary proxies significantly affected colon and total large intestine length only in non-phylogenetic analyses, suggesting patterns across, but not within, clades.

Conclusions:

• Dietary composition influences specific parts of the primate large intestine, but not overall gastrointestinal tract length or small intestine length.
• Phylogenetic history plays a crucial role in understanding diet-GIT relationships within primate clades.
• Primate large intestine lengths are longer than those of terrestrial Carnivora, but small intestine lengths are similar, indicating complex GIT adaptations beyond simple diet-GIT scaling.