Ecoevolutionary dynamics of the gut microbiota at the macroscale level, that is, in across-species comparisons, are largely driven by ecological variables and host genotype. The repeated explosive radiations of African cichlid fishes in distinct lakes, following a dietary diversification in a context of reduced genetic diversity, provide a natural setup to explore convergence, divergence and repeatability in patterns of microbiota dynamics as a function of the host diet, phylogeny and environment. Here we characterized by 16S rRNA amplicon sequencing the gut microbiota of 29 cichlid species from two distinct lakes/radiations (Tanganyika and Barombi Mbo) and across a broad dietary and phylogenetic range. Within each lake, a significant deviation between a carnivorous and herbivorous lifestyle was found. Herbivore species were characterized by an increased bacterial taxonomic and functional diversity and converged in key compositional and functional community aspects. Despite a significant lake effect on the microbiota structure, this process has occurred with remarkable parallels in the two lakes. A metabolic signature most likely explains this trend, as indicated by a significant enrichment in herbivores/omnivores of bacterial taxa and functions associated with fiber degradation and detoxification of plant chemical compounds. Overall, compositional and functional aspects of the gut microbiota individually and altogether validate and predict main cichlid dietary habits, suggesting a fundamental role of gut bacteria in cichlid niche expansion and adaptation.

BackgroundParasite switches to new host species are of fundamental scientific interest and may be considered an important speciation mechanism. For numerous monogenean fish parasites, infecting different hosts is associated with morphological adaptations, in particular of the attachment organ (haptor). However, haptoral morphology in Cichlidogyrus spp. (Monogenea, Dactylogyridea), parasites of African cichlids, has been mainly linked to phylogenetic rather than to host constraints. Here we determined the position of Cichlidogyrus amieti, a parasite of species of Aphyosemion (Cyprinodontiformes, Nothobranchiidae) in the phylogeny of its congeners in order to infer its origin and assess the morphological changes associated with host-switching events.MethodsThe DNA of specimens of C. amieti isolated from Aphyosemion cameronense in Cameroon was sequenced and analyzed together with that of Cichlidogyrus spp. from cichlid hosts. In order to highlight the influence of the lateral transfer of C. amieti on the haptoral sclerotised parts we performed a Principal Component Analysis (PCA) to compare the attachment organ structure of C. amieti to that of congeners infecting cichlids.ResultsCichlidogyrus amieti was found to be nested within a strongly supported clade of species described from Hemichromis spp. (i.e. C. longicirrus and C. dracolemma). This clade is located at a derived position of the tree, suggesting that C. amieti transferred from cichlids to Cyprinodontiformes and not inversely. The morphological similarity between features of their copulatory organs suggested that C. amieti shares a recent ancestor with C. dracolemma. It also indicates that in this case, these organs do not seem subjected to strong divergent selection pressure. On the other hand, there are substantial differences in haptoral morphology between C. amieti and all of its closely related congeners described from Hemichromis spp..ConclusionsOur study provides new evidence supporting the hypothesis of the adaptive nature of haptor morphology. It demonstrates this adaptive component for the first time within Cichlidogyrus, the attachment organs of which were usually considered to be mainly phylogenetically constrained.

The four Cichlidogyrus species (Monogenea, Ancyrocephalidae) found on the gills of Sarotherodon mvogoi and Tylochromis sudanensis (Teleostei, Cichlidae) in Cameroon are considered new and are described herein. Cichlidogyrus mvogoi n. sp. from Sarotherodon mvogoi, characterised by a long (> 100 µm), thin and spirally coiled penis and a short marginal hook pair I. Cichlidogyrus sigmocirrus n. sp. from Tylochromis sudanensis, characterised by a short marginal hook pair I, a slightly spirally coiled penis with reduced heel, an accessory piece being a spirally coiled band wrapped round the penis and attached to the penis basal bulb by a very thin filament. Cichlidogyrus chrysopiformis n. sp. from Tylochromis sudanensis, characterised by an marginal hook pair I of medium size, a thin spirally coiled penis (1.5 turn) with a developed flared heel, an accessory piece being a large gutter shaped band, ending in a narrow complex extremity, and linked to the basal bulb of the penis by a very thin filament, a short, straight and slightly ringed vagina. Cichlidogyrus djietoi n. sp. from Tylochromis sudanensis, characterised by a slightly spirally coiled penis (2 turns) with developed heel, an accessory piece being a large gutter shaped band, ending in a narrow folded back extremity, a short funnel shaped vagina. The three latter species are also remarkable by the morphology of their auricles implanted on the anterior side of the dorsal transverse bar which make them (together with the other species described from Tylochromis hosts) a homogeneous and original group within Cichlidogyrus, this distinctive feature seems to be ancestral compared to other Cichlidogyrus species.

Species of the monogenean genus Quadriacanthus mainly infect fish belonging to the Siluriformes, especially the genera Clarias, Heterobranchus or Bagrus, and their host specificity is strict (oioxenous) or narrow (stenoxenous). An examination of the gills of 19 Papyrocranus afer from Lake Ossa, South Cameroon, revealed for the first time the presence of a species of Quadriacanthus from a fish host belonging to the Notopteridae. The morphology and the size of sclerotized parts of haptor and the male and female copulatory complexes suggest that this monogenean is a new species named Quadriacanthus euzeti n. sp. The fish genus Papyrocranus differs taxonomically from the usual fish hosts of Quadriacanthus and hence the presence of a species belonging to this genus on the gills of this host suggests the occurrence of a lateral transfer of Quadriacanthus from species belonging to Clarias or Bagrus which live sympatrically with P. afer in Lake Ossa.

A checklist of the 23 species of Ancyrocephalidae (Monogenea) parasitizing Tilapia species sampled from both sides of the Cameroon Volcanic Line is provided. As already reported elsewhere, Cichlidogyrus aegypticus in Cameroon shows two different shape of its vagina, and C. tilapiae, C. arthracanthus and C. tiberianus were found on a wide range of host species. Among the 23 studied species of Monogenea, three are considered new species and are described herein: Cichlidogyrus berminensis n. sp. from Tilapia bemini, characterized by a short penis with marked narrow heel, a simple and straight accessory piece ending in a large hook, and a medium sized pair of uncinuli I; Cichlidogyrus gillesi n. sp. from Tilapia guineensis, characterized by a large and trapezoid heel of the penis and a S-shaped and wrinkle walled vagina; and Scutogyrus vanhovei n. sp. from Tilapia mariae, characterized by the presence of a distinct swollen portion of the penis. From a parasite's point of view, the CVL has no influence on species dispersion/distribution.