Adaptation, phylogeny, and covariance in milk macronutrient composition

Area of Science:

• Mammalian evolutionary biology
• Comparative physiology

Background:

• Milk macronutrient composition (fat, protein, sugar) is complex.
• Previous studies found limited ecological/life history influence, but a strong phylogenetic signal.
• Maternal diet is a key factor influencing milk composition.

Purpose of the Study:

• To re-examine ecological and life history correlates of milk macronutrient composition.
• To further elucidate the nature of the phylogenetic signal in milk traits.
• To identify mammal clades with unique milk compositions.

Main Methods:

• Multivariate phylogenetic comparative methods.
• Phylogenetic mixed models to assess phylogenetic signal.
• Nonparametric tests (KSI) and PhylogeneticEM for clade identification.

Main Results:

• Aquatic mammals exhibit milk lower in sugar and higher in fat.
• High phylogenetic heritabilities and moderate-to-strong phylogenetic correlations indicate trait coevolution.
• Primates, pinnipeds, perissodactyls, and marsupials show distinctive milk compositions.

Conclusions:

• Mammalian milk composition is diverse but often taxon-specific.
• Phylogenetic conservatism complicates traditional comparative analyses.
• Novel methods and a "phylogenetic natural history" approach are needed to understand milk evolution.