Diet disparity in the coexisting herbivorous cichlids in Lake Tanganyika revealed by metagenomics approach. gut metagenome

Lake Tanganyika, an ancient lake in Great Rift Valley, is famous for the adaptive radiation of cichlid fishes. Five tribes of the family (Tropheini, Lamprologini, Ectodini, Eretmodini, and Tilapini) have acquired herbivory, and show diversified feeding habits such as grazing, browsing, scraping, biting, and scooping. On a rocky littoral of the lake, 16 species of the herbivorous cichlids coexist. Seven of them individually defend feeding territory against intruding herbivores to establish algal farms where the territory-holder feeds on. We analyzed algal assemblages inside the territories defended by the herbivorous cichlids and stomach contents of 16 herbivorous cichlids by metagenomics approach. Based on 454-pyrosequencing of algal 16S rRNA sequences, we found 117 algal OTUs in total, that is, 76 cyanobacteria, 24 bacillariophytes, 14 chlorophytes, 2 streptophytes, and 1 ignavibacteria. Algal farms were different among cichlid species, and the difference was more than 50 percents in the algal composition. Stomach contents of the herbivorous cichlids were also segregated, at least more than 0.5 in the dissimilarity even between species in the same feeding habits. Dissimilarity in algal farms and that in stomach contents did not differ between the same-tribe pairs and different-tribe pairs, and did not differ between the same feeding-habit pairs and the different feeding-habit pairs. These results clearly show that these herbivorous cichlids segregate their diet both among phylogenetically close species and among ecologically similar species. In this way, metagenomics approach successfully reveals food niche separation among all the coexisting herbivorous cichlids in a rocky shore of Lake Tanganyika.