Color polymorphism in an aphid is maintained by attending ants

Area of Science:

• Ecology
• Evolutionary Biology
• Entomology

Background:

• Polymorphism enhances understanding of phenotypic and genetic diversity.
• Balancing selection typically explains the persistence of polymorphism.
• Color polymorphisms in insects are often maintained by balancing selection, such as frequency-dependent predation.

Purpose of the Study:

• To investigate the selective advantages of two color morphs (red and green) in the ant-attended aphid, Macrosiphoniella yomogicola.
• To determine if traditional balancing selection explains color polymorphism in aphids protected from predation by ants.
• To examine the role of ant attendance in maintaining color polymorphism.

Main Methods:

• Field study of Macrosiphoniella yomogicola colonies with varying proportions of red and green morphs.
• Quantification of ant attendance on aphid colonies.
• Analysis of the relationship between ant attendance and morph proportions, controlling for colony sizes.

Main Results:

• Ants showed a strong preference for aphid colonies with intermediate proportions of red and green morphs.
• The relationship between ant attendance and morph proportion exhibited a convex curve, peaking at approximately 65% green morphs.
• Aphid colonies free from predation were maintained by a symbiotic relationship with ants.

Conclusions:

• The study presents the first case of balancing polymorphism maintained by a symbiotic relationship rather than opposing factors.
• Ant attendance, driven by intermediate morph proportions, acts as the selective advantage for maintaining color polymorphism in this aphid species.
• This finding offers a new perspective on the mechanisms driving the evolution and maintenance of genetic diversity.