Coevolution and Genetic Divergence Between Two Aphid Species (Aphididae, Lachninae: Cinara formosana and Tuberolachnus salignus) and Their Obligate Buchnera Symbionts

The obligate symbiosis between aphids and their primary bacterial symbionts (Buchnera) is ecologically and evolutionarily significant, yet the genetic patterns underlying these associations require further clarification. This study investigated the coevolutionary relationships of two aphid species, Cinara formosana and Tuberolachnus salignus, with their Buchnera symbionts using COI (mitochondrial cytochrome c oxidase subunit I) and bacterial 16S rRNA (16S ribosomal RNA) markers revealed substantial genetic divergence between the two aphid species, with interspecific genetic distances ranging from 0.131 to 0.138. In contrast, populations of T. salignus from different regions showed minimal intraspecific variation (genetic distance 0.006). Phylogenetic analyses confirmed that populations of each aphid species formed distinct, monophyletic clusters. Crucially, the phylogenetic relationships inferred from the aphid COI gene were fully congruent with those derived from the Buchnera 16S rRNA gene sequences. This concordance further supports the application of the COI gene as a reliable marker for species identification within the studied Lachninae aphids. Our findings provide novel insights into the coupled genetic divergence and coevolution of aphids and their obligate symbionts, offering a molecular framework for the precise identification and population monitoring of these aphids, which can inform sustainable management strategies.