Metagenomic Insights Into the Dietary Diversity of the Adaptive Radiation of Cichlid Fishes in Lake Tanganyika.

Diet specialisation is a main driver of diversification in many adaptive radiations. Therefore, identifying diet items is essential to characterise trophic specialisations and to understand the dynamics of dietary adaptations. In this study, we explored the trophic niches of 56 species from the adaptive radiation of cichlid fishes in Lake Tanganyika, encompassing all major phylogenetic lineages and feeding specialisations. We employed a metagenomic sequencing approach to identify the food sources of the investigated species at high taxonomic resolution, sequencing over 400 digestive content samples from wild-caught individuals at around 50 million paired-end read depth per sample. Our analyses revealed Arthropoda, Chordata (fishes), Bacillariophyta and Streptophyta as the primary diet phyla of the Tanganyikan cichlids. Moreover, we confirmed the presence of other food sources and identified taxa not previously documented to be part of the cichlids' diet. Based on their dietary compositions, the Tanganyikan cichlids can be grouped into herbivores, invertivores, piscivores and mixed feeders. Further, we showed that trophic disparity in the radiation is shaped by rapid divergence and documented cases of dietary niche convergence. Diet composition correlated with carbon and nitrogen stable isotope values, gut length, and body morphology. Differences in diet-such as the consumption of diatoms, streptophytes and chlorophytes versus fish and arthropods-were associated with changes in body, upper oral jaw and lower pharyngeal jaw shape. Collectively, this study presents a comprehensive and detailed diet classification of the Tanganyikan cichlids, highlighting the power of metagenomic approaches in delineating dietary adaptations.