Wolbachia-centered cytoplasmic axis links elevational mitochondrial DNA turnover with microbiome restructuring

Mountain gradients act as natural experiments, and elevational mitochondrial DNA clines in insects are often interpreted as signatures of local metabolic adaptation. However, mitochondrial DNA is maternally co-inherited with heritable endosymbionts that can promote cytoplasmic hitchhiking and, when abundant, dominate marker-gene microbiome profiles, complicating inference about environmental forcing. Here, we evaluate a symbiont-aware cytoplasmic-axis framework in the tea green leafhopper Empoasca onukii using a densely replicated elevational survey across tea agroecosystems. Across 790 adults from 79 sites spanning 11 to 2750 meters above sea level, we quantified Wolbachia infection prevalence, within-host burden, and strain composition, and related these measures to mitochondrial haplotypes, a conservative nuclear reference marker, and whole-insect bacterial community profiles. Wolbachia prevalence, burden, and strain composition varied along elevation, with pronounced strain turnover. Mitochondrial diversity declined and haplotypes homogenized at high elevations, whereas the nuclear reference marker showed weak spatial structure, yielding mitochondrial-nuclear discordance consistent with cytoplasmic hitchhiking and sweep-like mtDNA homogenization. Bacterial community separation was strongest when Wolbachia features were retained but persisted after Wolbachia removal and renormalization, indicating both compositional dominance by Wolbachia and residual restructuring among non-Wolbachia taxa. In a balanced subset, mitochondrial coding variation and host energetic readouts provided observational functional context for the Wolbachia-centered cytoplasmic-axis pattern. Together, these results place Wolbachia at the center of a testable cytoplasmic framework linking elevational mitochondrial turnover with microbiome restructuring, and they highlight the broader importance of dominant heritable symbionts.