Haplotaxodon

Abstract: Cichlid fishes in Lake Tanganyika exhibit remarkable diversity in their feeding habits. Among them, seven species in the genus Perissodus are known for their unique feeding habit of scale eating with specialized feeding morphology and behaviour. Although the origin of the scale-eating habit has long been questioned, its evolutionary process is still unknown. In the present study, we conducted interspecific phylogenetic analyses for all nine known species in the tribe Perissodini (seven Perissodus and two Haplotaxodon species) using amplified fragment length polymorphism (AFLP) analyses of the nuclear DNA. On the basis of the resultant phylogenetic frameworks, the evolution of their feeding habits was traced using data from analyses of stomach contents, habitat depths, and observations of oral jaw tooth morphology. AFLP analyses resolved the phylogenetic relationships of the Perissodini, strongly supporting monophyly for each species. The character reconstruction of feeding ecology based on the AFLP tree suggested that scale eating evolved from general carnivorous feeding to highly specialized scale eating. Furthermore, scale eating is suggested to have evolved in deepwater habitats in the lake. Oral jaw tooth shape was also estimated to have diverged in step with specialization for scale eating. The present evolutionary analyses of feeding ecology and morphology based on the obtained phylogenetic tree demonstrate for the first time the evolutionary process leading from generalised to highly specialized scale eating, with diversification in feeding morphology and behaviour among species.

Abstract: LAKE Tanganyika, one of the Great Rift Valley lakes in central east Africa, is famous for the high levels of endemism among the cichlid fishes and some other animal groups (Coulter, 1991; Fryer, 1991). The monotypic cichlid genus Haplotaxodon Boulenger, 1906, also endemic to the lake, is quite distinct from other cichlid genera of the lake by the possession of a mouth which is directed upward and a single row of conical teeth on the jaws (Boulenger, 1906; Regan, 1920; Poll, 1986). During a series of scientific surveys of Lake Tanganyika, specimens of an undescribed species of Haplotaxodon were collected at various localities in the lake (Fig. 1).