Color polymorphism in an aphid is maintained by attending ants.
The study of polymorphisms is particularly informative for enhancing our understanding of phenotypic and genetic diversity. The persistence of polymorphism in a population is generally explained by balancing selection. Color polymorphisms that are often found in many insects and arthropods are prime examples of the maintenance of polymorphisms via balancing selection. In some aphids, color morphs are maintained through frequency-dependent predation by two predatory insects. However, the presence of color polymorphism in ant-attended aphids cannot be explained by traditional balancing selection because these aphids are free from predation. We examined the selective advantages of the existence of two color (red and green) morphs in the ant-attended aphid, Macrosiphoniella yomogicola, in fields. We measured the degree of ant attendance on aphid colonies with different proportions of color morphs. The results show that the ants strongly favor aphid colonies with intermediate proportions of the two color morphs. The relationship between the degree of ant attendance and the proportion of color morphs in the field is convex when aphid colony size and ant colony size are controlled. This function has a peak of approximately 65% of green morphs in a colony. This system represents the first case of a balancing polymorphism that is not maintained by opposing factors but by a symbiotic relationship.
Laboratory of Animal Ecology, Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Saori
S
Watanabe
Laboratory of Animal Ecology, Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Taiga
T
Murakami
Graduate School of Science and Technology and Department of Mathematical and Systems Engineering, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Japan.; Marine Biosystems Research Center, Chiba University, Uchiura, Kamogawa, Chiba 299-5502, Japan.; Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse, NY 13210, USA.
Jin
J
Yoshimura
Laboratory of Animal Ecology, Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Eisuke
0000-0002-5782-4225
E
Hasegawa
D000818:Animals; D001000:Ants / Q000235:genetics / Q000502:physiology; D001042:Aphids / Q000235:genetics / Q000502:physiology; D014644:Genetic Variation; D007313:Insecta / Q000235:genetics / Q000502:physiology*; D010858:Pigmentation / Q000235:genetics*; D011157:Population Dynamics; D011235:Predatory Behavior / Q000502:physiology; D012641:Selection, Genetic / Q000235:genetics*; D013559:Symbiosis / Q000235:genetics / Q000502:physiology
Polymorphism; ant attendance; aphids; balancing selection; color morphs; frequency dependent selection