Genetic Differentiation between Color Morphs of a Color-Polymorphic Aphid Macrosiphoniella yomogicola

Maintenance of intraspecific polymorphisms is important for biodiversity. The aphid Macrosiphoniella yomogicola has two color morphs (green and red) in Hokkaido. Their primary attending ants (Lasius japonicus) can manipulate the frequency of the green morph to match that of the red morph to maintain the polymorphism in an aphid colony. Ants prefer the green morph owing to its high-quality honeydew; however, the ants intentionally maintain nutritionally inferior red morphs in every colony because the ants only manipulate the reproductive rate of the green morph, i.e., the ants discriminate between the two morphs. Thus, the benefit of the red morphs to the ants should differ from nutrient exploitation. This hypothesis requires a genetic trade-off between the two morphs. Here based on three microsatellites, we show that the genetic distance between both morphs collected from the same sampling site is small suggesting that there is no genetic differentiation between their whole genomes. However, there were significant differences between the two morphs at a locus at the three sites examined. Our results suggest that intermorph copulations occur; however, the loci controlling morph-specific traits should be linked with the differentiated locus.