Insects have an eye for symmetry
Eating one’s greens is all well and good, but some greens are tastier than others. New research shows that leaf-munching insects are far fussier eaters than one might think – they will even pick and choose leaves on the basis of how symmetrical they are.
Biologists in Finland have found that of 11 species of herbivorous caterpillars and beetle larvae, nine show a significant preference for either symmetrical or lopsided leaves. Some species on certain trees prefer symmetrical leaves, while other species on different trees prefer lopsided ones.
Higher asymmetry in biological structures that are normally symmetrical may indicate mistakes in the developmental process. In some cases, asymmetrical leaves may be less well defended with natural insecticides, making them an attractive menu option. In others, they may lack nutritional value, and be rejected.
It’s not clear how the insects can tell how symmetrical a leaf actually is. One possibility is that they are detecting chemical differences between symmetrical and asymmetrical leaves. But there’s also evidence that the bugs are measuring the degree of symmetry directly. “One of the species used in our experiments explores leaf shape by walking around the leaf,” write the scientists. SB
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