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In Memory of Bill Hamilton

A Day in Taiwan by Shigeyuki Aoki

On 22 July 1986, Bill Hamilton and I, together with Naomi Pierce and Andrew Berry, visited Sun Moon Lake, central Taiwan. The main purpose of the trip was to show him live aphid-soldiers, in particular, soldiers of the aphid Ceratoglyphina styracicola, which forms white galls on the evergreen Styrax suberifolia. It was a nice summer day. After walking around the beautiful lake, we eventually found a good tree harboring many galls, but at a height of about 5 m above the ground. He went into the bush without hesitation, and skillfully climbed the tree. Because of my inability to climb up, I wished I could hire him as a climber for my research. He cut off a branch with several galls and took them carefully down to the ground. He then made two galls, one of which had been collected from another tree, in contact with each other. There were many soldiers on the surfaces of the two galls. He watched what would happen when soldiers of one gall encountered soldiers of the other. Nothing happened, however, and this was what I had expected from my previous experience.

He was not satisfied with the fact that no war broke out, or that soldiers of C. styracicola did not discriminate between clonemates and non-clonemates. He told me that the experiment was not sufficient, and suggested another experiment: Watch what will happen when soldiers of one gall encounter non-soldiers from another gall. I did not take the suggestion seriously. Nor did he put his idea in practice, although we could have done it on that day.

Four years later, I found a very good gall for observation. It was formed at a height of 1.5 m. I felt compelled to do something, and my wife and I agreed to carry out that very experiment. Soldiers of the gall did not attack any soldiers placed on the gall surface as usual, but did attack all non-soldiers taken from other galls. On the gall surface, soldiers even attacked non-soldiers taken from the gall itself. This means that soldiers of C. styracicola discriminate between soldiers and non-soldiers, and is a strong positive evidence for the hypothesis that aphid soldiers cannot discriminate between kin and non-kin, or between clonemates and non-clonemates.

When I was writing our 1991 paper on the discrimination between soldiers and non-soldiers, I completely forgot that the key idea had come from Bill Hamilton. I should have thanked him in the paper, though he would not care about this.