Microbiota Anatomical Niche Partitioning of Simulium vanluni (Diptera: Simuliidae)

Background: Microbial communities of insects have distinct roles for their respective hosts. For the black fly (Diptera: Simuliidae), an important vector and ecological indicator, the representative microbiota from the different body regions are not known. Here, we investigated the microbial composition and diversity of the head, thorax, and abdomen of wild-caught Simulium vanluni. Methods: Adult Simulium vanluni were surface-sterilized and dissected into head, thorax, and abdomen. For each body region, 20 individuals were pooled into one sample with six replicates per region. DNA was extracted and sequenced using the 16S rRNA amplification method to assess for possible microbial diversity. Data were analyzed using MicrobiomeAnalyst, where we calculated alpha diversity, beta diversity, and tested compositional differences using PERMANOVA. Results: Across 17 pooled samples, three core genera, Wolbachia (78.33%), Rickettsia (9.74%), and Acinetobacter (9.20%), accounted for more than 97% of the 16S rRNA sequencing reads. Head communities were compositionally distinct compared to the thorax and abdomen (PERMANOVA, p < 0.05). Heads were nearly monodominated by Wolbachia (95–97%), exhibiting significantly lower diversity and evenness compared to other body regions. In contrast, the thoracic and abdominal communities were more even, where thoraces were enriched with Acinetobacter (19.16%) relative to Rickettsia (10.85%), while abdomens harbored higher Rickettsia (10.96%) than Acinetobacter (5.68%). Collectively, the near-monodominance of Wolbachia in heads and inverse abundances of Acinetobacter and Rickettsia in thoraces and abdomens suggest possible anatomical niche partitioning or competition exclusion of microbiota across body regions. Conclusions: Our findings reveal fine-scale anatomical niche partitioning in S. vanluni microbiota, with the heads being almost exclusively colonized by Wolbachia, while the thoracic and abdominal niche regions exhibit distinct enrichment patterns for Acinetobacter and Rickettsia. These spatially distinct microbial distributions suggest potential functional specialization across anatomical regions of S. vanluni.