Adaptive radiations reveal ecological opportunity and incumbency as drivers of dietary niche evolution in Papua New Guinea rodents
New Guinea (NG) hosts one of the world's most remarkable rodent radiations: two native tribes; the ancient Hydromyini (~8.5–7 Ma) and the endemic Rattini (~2.4–1.3 Ma) colonised the island under contrasting ecological conditions, alongside recent human-mediated introductions of invasive Rattus. Using 18S rRNA metabarcoding of gut contents from 819 individuals spanning 44 species across two altitudinal transects in Papua New Guinea (PNG), integrated with a ddRAD-based phylogeny, we characterised dietary niches across the most comprehensive sampling to date and reconstructed their evolutionary history. Dietary composition showed a strong phylogenetic signal, indicating that trophic identity is inherited rather than environmentally determined. Hydromyini diversified from a herbivorous ancestor into the full range of trophic guilds (omnivory, fungivory, and herbivory) consistent with ecological opportunity. In contrast, endemic Rattini colonised an island already occupied by diverse Hydromyini and diversified into partially vacant niches: omnivory (Rattus niobe, R. steini) and fungivory (R. verecundus), consistent with incumbency-driven niche compression. Niche breadth was likewise phylogenetically conserved, yet individual diets still varied along local environmental gradients, broad dietary strategy is inherited, while individual flexibility tracks local conditions. Individuals sharing a locality had more similar diets, but this convergence was weaker between species than within species, indicating that co-occurring species maintained distinct diets through niche differentiation. Invasive Rattus showed a diet based on anthropogenic sources, exhibiting the most restricted niches in the community. These findings support the ecological opportunity with incumbency model as a central driver of dietary diversification in NG rodents.
New Guinea (NG) hosts one of the world's most remarkable rodent radiations: two native tribes; the ancient Hydromyini (~8.5–7 Ma) and the endemic Rattini (~2.4–1.3 Ma) colonised the island under contrasting ecological conditions, alongside recent human-mediated introductions of invasive Rattus. Using 18S rRNA metabarcoding of gut contents from 819 individuals spanning 44 species across two altitudinal transects in Papua New Guinea (PNG), integrated with a ddRAD-based phylogeny, we characterised dietary niches across the most comprehensive sampling to date and reconstructed their evolutionary history. Dietary composition showed a strong phylogenetic signal, indicating that trophic identity is inherited rather than environmentally determined. Hydromyini diversified from a herbivorous ancestor into the full range of trophic guilds (omnivory, fungivory, and herbivory) consistent with ecological opportunity. In contrast, endemic Rattini colonised an island already occupied by diverse Hydromyini and diversified into partially vacant niches: omnivory (Rattus niobe, R. steini) and fungivory (R. verecundus), consistent with incumbency-driven niche compression. Niche breadth was likewise phylogenetically conserved, yet individual diets still varied along local environmental gradients, broad dietary strategy is inherited, while individual flexibility tracks local conditions. Individuals sharing a locality had more similar diets, but this convergence was weaker between species than within species, indicating that co-occurring species maintained distinct diets through niche differentiation. Invasive Rattus showed a diet based on anthropogenic sources, exhibiting the most restricted niches in the community. These findings support the ecological opportunity with incumbency model as a central driver of dietary diversification in NG rodents.