A new species of copepod, Styelicola omphalus n. sp., of the family Ascidicolidae is described as an associate or symbiont of the ascidian Phallusia nigra Savigny, 1816 from the Red Sea. As major differential features of the new species, the body is large, more than 4 mm long, the antennule is 5-segmented, the mandibular palp is armed with one or two apical setae, and the maxillary syncoxa, maxilliped, and endopods of legs 1-4 are unarmed. This is the first confirmed ascidicolid reported from the Red Sea. Supplementary descriptions for two additional copepods from the same host, but in the family Notodelphyidae, are provided. Males of Bonnierilla projecta Stock, 1967 and Janstockia phallusiella Boxshall and Marchenkov, 2005 are detailed for the first time. The occurrence and location of the three species of copepods differed within the host. Styelicola omphalus was found in approximately 3% of hosts examined, consistently attached to the visceral mass. Bonnierilla projecta, in contrast, occurred in 63% of hosts and was located in the pharyngeal sac, and J. phallusiella was found attached to the internal surface of the tunic (atrium) in 11% of the hosts examined. Although the ascidian P. nigra has a circumtropical distribution, the copepods discussed above have only been reported from the Red Sea. Approximately 25 species of copepods are known as associates of Phallusia worldwide, but these appear restricted to only three (possibly five) of the 20 species currently recognized in this ascidian genus.

Background The continuous proliferation of intestinal stem cells followed by their tightly regulated differentiation to epithelial cells is essential for the maintenance of the gut epithelial barrier and its functions. How these processes are tuned by diet and gut microbiome is an important, but poorly understood question. Dietary soluble fibers, such as inulin, are known for their ability to impact the gut bacterial community and gut epithelium, and their consumption has been usually associated with health improvement in mice and humans. In this study, we tested the hypothesis that inulin consumption modifies the composition of colonic bacteria and this impacts intestinal stem cells functions, thus affecting the epithelial structure. Methods Mice were fed with a diet containing 5% of the insoluble fiber cellulose or the same diet enriched with an additional 10% of inulin. Using a combination of histochemistry, host cell transcriptomics, 16S microbiome analysis, germ-free, gnotobiotic, and genetically modified mouse models, we analyzed the impact of inulin intake on the colonic epithelium, intestinal bacteria, and the local immune compartment. Results We show that the consumption of inulin diet alters the colon epithelium by increasing the proliferation of intestinal stem cells, leading to deeper crypts and longer colons. This effect was dependent on the inulin-altered gut microbiota, as no modulations were observed in animals deprived of microbiota, nor in mice fed cellulose-enriched diets. We also describe the pivotal role of γδ T lymphocytes and IL-22 in this microenvironment, as the inulin diet failed to induce epithelium remodeling in mice lacking this T cell population or cytokine, highlighting their importance in the diet-microbiota-epithelium-immune system crosstalk. Conclusion This study indicates that the intake of inulin affects the activity of intestinal stem cells and drives a homeostatic remodeling of the colon epithelium, an effect that requires the gut microbiota, γδ T cells, and the presence of IL-22. Our study indicates complex cross kingdom and cross cell type interactions involved in the adaptation of the colon epithelium to the luminal environment in steady state.

Despite a rich taxonomic literature on the symbionts of ascidians, the nature of these symbioses remains poorly understood. In the Egyptian Red Sea, the solitary ascidian Phallusia nigra hosted a symbiotic amphipod and four copepod species, with densities as high as 68 mixed symbionts per host. Correlation analyses suggested no competition or antagonism between symbionts. Ascidian mass, ash-free dry mass per wet mass (AFDM/WM), and both symbiont density and diversity per host, differed significantly among three reefs from El Gouna, Egypt. However, there was no correlation between amphipod, total copepod, or total symbiont densities and host mass or AFDM/WM. A host condition index based on body to tunic mass ratio was significantly related to symbiont density overall, but this positive pattern was only strong at a single site studied. Despite assumptions based on the habit of some of the symbiont groups, our analyses detected little effect of symbionts on host health, suggesting a commensal relationship.

No abstract