Narrow-range genetic structuring of a tree trunk-using sedentary aphid Stomaphis yanonis (Hemiptera: Aphididae)

The geographic scale of population genetic structure varies widely among species and is shaped not only by geographic barriers but also by ecological and life-history traits that constrain dispersal. While many aphid species disperse widely through frequent production of winged morphs, species with severely limited dispersal are expected to develop pronounced genetic structuring even across short distances. We investigated fine-scale population genetic structure in Stomaphis yanonis aphids whose traits restrict dispersal and establishment: they are highly sedentary aphids that feed on phloem sap from tree trunks using an extremely long proboscis and depend on obligate mutualism with ants. We sampled nine populations inhabiting Celtis sinensis trees (maximum distance 5.2 km) and conducted single-nucleotide polymorphism-based genetic analyses. The analyses detected genetic structuring not only between two geographically separated groups defined along an east–west axis (an eastern group consisting of three host trees and a western group consisting of six host trees, separated by 4 km), but also among populations within the western group, where host trees were separated by 0.73 km. Isolation-by-distance analysis within the western group did not detect a significant relationship between genetic differentiation and geographic distance. Relative migration analyses suggested that most pairwise connections were weak, with few directional connections showing comparatively high values. These results suggest that distinct fine-scale genetic structuring can arise even among nearby aphid populations without obvious geographical barriers, and are consistent with the interpretation that the sedentary life history of S. yanonis and its severely limited dispersal contribute to localized genetic differentiation.