Contrasting patterns of genetic structure and dispersal ability in ant-attended and non-attended Tuberculatus aphids

Aphid species within the genus Tuberculatus exhibit a variety of interactions with ants, ranging from close associations to non-attendance. An ant-attended species, Tuberculatus quercicola, and two non-attended species, Tuberculatus japonicus and Tuberculatus paiki, are sympatric and hosted by the tree species Quercus dentata (Fagaceae). An undescribed ant-attended species of Tuberculatus (sp. A) and several non-attended Tuberculatus species are found on Quercus crispula trees. The population genetic structure was examined for the species sympatric on 11 Q. dentata trees and on 11 Q. crispula trees using five microsatellite loci. To determine the extent to which ant-attended or non-attended species migrate between subpopulations, flight intercept traps were placed in the study sites. Ant-attended species exhibited lower allelic richness and showed increased genetic differentiation between subpopulations compared with those of non-attended species. The number of non-attended species caught in traps increased with seasonal abundance; however, few ant-attended species were trapped, despite their abundance. These results suggest that populations of ant-attended aphids are composed of fragmented local subpopulations that are connected by low dispersal rates, leading to considerable population differentiation.