Mammalian guts harbor indigenous microbes that are integral to host health. Microbiome research using sophisticated model organisms has provided insights into intricate interactions between microbiota and host animals. However, it remains unclear how these animal-microbe associations developed. We have recently addressed this question via comparative analyses of chordates, given that complex biological systems can be resolved into ancestral and derived elements when examined in an evolutionary framework (Nat Commun 9: 3402). Results support the view that microbial colonization of the mucus layer that overlies mammalian gastrointestinal epithelium was established upon loss of ancestral chitin-based barrier immunity. Comparative approaches enable us to arrange ongoing biological processes into host natural history for better understanding of intestinal animal-microbe associations.
Keywords: chitin; chordates; co-evolution; gut; microbiota; mucosal immunity; mucus layer.