AsianScientist (Feb. 19, 2018) – In a study published in Scientific Reports, a team of researchers in Japan have discovered that ants can tweak the reproductive success of aphids to their benefit.
Ants and aphids coexist in a symbiotic relationship that benefits both species. Ants protect aphids from predators, such as lady bugs and wasps, and aphids secrete nutritious honeydew for ants to eat. The aphid species Macrosiphoniella yomogicola comes in two morphs with distinct colors: red and green.
Typically, competition for survival would lead to one morph of aphid dominating the other. However, this rule can be broken in a few circumstances, including if an ant benefits from maintaining a mixture of color morphs.
Previously, Associate Professor Eisuke Hasegawa of Hokkaido University, Japan, and his colleagues had determined that Lasius japonicus ants prefer the nutrient-rich honeydew produced by green aphids. They also found that ants were most attracted to and most vigorously protected colonies with 65 percent green and 35 percent red aphids.
In this study, Hasegawa found that ants actively manipulate aphid populations by improving the reproduction rate of the inferior morph. In field experiments where the ants were absent, the red morphs had a much higher and superior reproduction rate than green morphs. Thus, red aphids should dominate. However, when ants were introduced to the experiment, the green morph reproduction rate equalized with the red morphs.
The experimental evidence matches what researchers find in the wild—red and green morphs coexisting on the same plant shoots attended by ants. What remains a mystery is this: if the ants prefer the green morphs’ honeydew, why keep the red morphs around at all?
“We theorize that the red morphs are able to provide a benefit that the green morphs can’t, such as suppressing the development of lower buds on host plants. This might help both the red and green aphids survive and reproduce more throughout the year, which could maximize long-term harvesting of honeydew from the green aphids,” Hasegawa explained.
“In this case, the ants invest in a future benefit by sacrificing the present benefit,” the researchers hypothesized.
The article can be found at: Watanabe et al. (2018) Ants Improve the Reproduction of Inferior Morphs to Maintain a Polymorphism in Symbiont Aphids.
Source: Hokkaido University; Photo: Ryota Kawauchiya.
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