Comparative analysis of morphology and gut microbiome underlying trophic niche differentiation in three stomatopod species.

Given that predatory strategies and trophic niche in stomatopods vary with raptorial appendage differentiation, a comparative analysis was conducted on three species (Odontodactylus japonicus, Lysiosquilla sulcirostris, and Oratosquilla oratoria) exhibiting distinct habitats and morphologies. The study measured their raptorial appendage morphology, digestive tract morphology, and gut microbiota. The results revealed significant differences in the raptorial appendages and digestive tract morphology among the three stomatopod species. O. japonicus has the significantly largest merus length, merus width, merus height and, L. sulcirostris has the significantly largest propodus length, dactylus length, hepatopancreas length and midgut length, while O. oratoria has the significantly largest hindgut length, cardiac stomach length and pyloric stomach length. Regarding digestive tract morphology, O. japonicus possessed the widest villus and tallest villus, in contrast to O. oratoria, which displayed the smallest values for these features. A total of 8,273 operational taxonomic units (OTUs) were obtained from all 16S rRNA sequences. The OTU numbers for O. oratoria, L. sulcirostris, and O. japonicus were 344, 113, and 82, respectively, with only 17 OTUs shared among all three species. The gut microbiota of O. japonicus was dominated by the phylum Pseudomonadota (88.90%), primarily comprised of the genus Cupriavidus (68.40%). In contrast, the dominant phylum in both L. sulcirostris and O. oratoria was Bacillota, with Mycoplasma being the dominant genus in each, respectively. Furthermore, O. oratoria exhibited the highest gut microbial diversity, whereas L. sulcirostris had the lowest. Functional profiling revealed that the relative abundance of gut microbiota associated with amino acid, lipid, and carbohydrate metabolism was significantly higher in O. japonicus than in both O. oratoria and L. sulcirostris. In conclusion, our findings provide further evidence for feeding habit differentiation and associated regulatory mechanisms among the three stomatopod species. The high gut microbial diversity in O. oratoria may contribute to its adaptability to the dynamic, heterogeneous habitats it occupies. Although the microbial abundance in O. japonicus is intermediate between that of O. oratoria and L. sulcirostris, its microbiota appears to be more efficient in digestive function, particularly in the metabolism of key nutrients. This study systematically elucidates the regulatory mechanisms underlying trophic niche differentiation in stomatopods from integrated morphological and physiological perspectives. Our findings provide a valuable foundation for future research on the evolution of higher taxonomic groups within Stomatopoda based on nutritional ecology.