By MASAHIRO YONEYAMA/ Staff Writer
August 11, 2020 at 18:59 JST
A high school teacher trying to solve the mystery of why queen Vespula wasps mate with many different males thinks the practice might have evolved to stave off a catastrophic colony collapse.
Tatsuya Saga, a teacher at Gifu prefectural Tajimi High School and a special cooperative researcher at Gifu University, led a study into the matter, which was recently published at the online edition of the international journal Behavioral Ecology.
The research team hypothesizes that the queen wasps’ copulation patterns are a result of evolution to prevent diseases from killing off their colonies.
It is common for a queen bee or ant to mate with a male once in her life. Repeated mating increases the risk for queens to become infected with sexually transmitted diseases or for being eaten by enemies outside the nest.
But the reason for multiple mating is still not very well understood. One theory is that it leads to genetic diversity, so that the colony is better protected from various diseases--something that has been demonstrated in some bees and ants.
Saga considered this theory when breeding polyandrous Vespula shidai wasps died due to molds.
He was able to obtain assistance from the insect enthusiasts in and around Gifu Prefecture, an area where locals eat larva collected from wasp nests as a longtime practice.
Saga obtained disease-causing fungi from dead wasps. Saga bred about 600 wasps across three nests, and infected them with different kinds of fungi and studied how long they lived.
He discovered that survival rates differ depending on their paternity, and the kind of fungus they were exposed to. Some wasps have strong resistance to a given fungus. Others have weak resistance to one type of fungus but have strong resistance to others.
The authors suggest genetic diversity in the colony developed to prevent a disease outbreak that would threaten the colony’s survival, a situation where the wasps die out all at once in their crowded nests, caused by just one type of disease.
“Wasps in the nests had genetically diverse disease resistance,” Saga said. “I can assume that Vespula shidai developed the practice of mating with multiple partners to gain such a genetic diversity.”
Vespula wasps make their nests underground, making them prone to attract germs.
“Their nests are more likely to be infected with germs, and such an environment might have had an effect on the evolution of their mating practices,” he said.
Saga said that he plans to continue his research.
The paper can be read at the website: (https://doi.org/10.1093/beheco/araa062).
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