Now they have published new research in the journal Biology Letters that shows that some paper wasps — those that have variable facial patterns recognized by other wasps in the nest — have more acute vision relative to their size than do wasps without variable facial patterns.
The paper wasps with variable facial patterns are mostly species in which several queens sometimes cooperate to establish a colony, which would make the ability to discriminate among individuals important, he said. Depending on the species, wasps have evolved facial markings that act either like name tags for individual recognition, or like karate belts that indicate a queen’s strength.
“Larger facets in their compound eyes mean better vision, but we found that as these wasps get smaller, they have larger than expected eyes,” Sheehan said. “This demonstrates that they evolved improved acuity relative to size in order to discriminate among different individuals in the colony.”
Like all insects, paper wasps have compound or faceted eyes, each a cluster of thousands of small, telescope-like omatidia with an outer lens that focuses light onto sensory cells inside the eye.
Compound eyes are great for detecting motion — hence a fly’s ability to dodge a swatter — but they provide poor resolution, though larger diameter lenses collect more light and generally provide sharper vision. Many flying insects have a high-acuity zone within the compound eye outfitted with larger diameter lenses and typically facing forward.
Sheehan reasoned that if patterns on the face were important for wasp social interactions, then natural selection might favor wasps that see better, and the lenses in the high-acuity zone on smaller species would be disproportionately larger.
That is what he found when surveying 19 different species of paper wasp in the genus Polistes, half of which were caught in fields around the East and the Midwest, and half obtained from museum collections, some of which were more than 100 years old. While the largest lenses on the eyes of big wasps were the same size — whether or not the wasps could recognize facial patterns — smaller wasps differed. Those with variable facial patterns had larger lenses in their acute zone than those that do not have variable faces.
“This doesn’t overturn evolutionary dogma, but extends the idea that feedback from the environment — in this case, communication signals among members of the same species — can drive change in our senses,” Sheehan said.
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