October 4, 2023

Spider mite males “undress” their mates to mate as quickly as possible

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You can’t rush love,” the Supremes chanted, but in the animal kingdom finding a potential mate as soon as possible can be crucial to gene passing.

Researchers described an extreme example of this behavior in a new study published Friday in the journal iScience: Male spider mites peel the molting skin off newly matured females to ensure they are first in line to mate.

Spider mites are tiny arachnids, distant cousins ​​of spiders, smaller than the tip of a standard ballpoint pen. These eight-legged creatures live in large groups and feed on plants by piercing the tissues with their sharp mouthparts and sucking out the juices.

Living together in dense colonies can lead to fierce competition for mates, especially since female spider mites only use the sperm of the first male they mate with. They even store this sperm in a special internal pouch to fertilize their eggs for the rest of their lives.

Since mating first with a female is the only way for a spider mite to pass on its genes, males have developed strategies to increase their chances. Males guard females that are almost fully grown so that once the females are ready to mate, the males are ready. Some males fight off competitors approaching the nearly mature females, while others, dubbed “sneakers” by researchers, lie in wait stealthily. Once the female sheds her old skin and emerges as a mature adult, the males charge in.

Molting and mating

Dr. Peter Schausberger, principal investigator of arthropod behavioral ecology and lecturer at the University of Vienna, studies the mating behavior of spider mites. He and his colleagues were viewing video footage taken with a digital microscope when they noticed something strange happening.

“We observed that the guarding male becomes very active and starts tugging at the female’s skin and pulling it off,” said Schausberger, the lead author of the new paper. “The males then pull off the back parts (of the skin) to access the genital opening” to do the deed. “Sometimes they copulate with the front part (of the female) still covered,” he said — there’s no time to undress completely.

The process may sound gruesome, but Schausberger said it doesn’t hurt the females — the skin the males peel off is dead and would come off on its own without their help.

Schausberger and his colleagues studied the mites’ undressing behavior in the lab. The team found that when the males helped the females remove their old skin, the molting process was speeded up and the males’ chances of mating first were maximized. “Even a few minutes early, it pays off for the guard man not to lose his guard investment to another,” Schausberger said.

Although this research was limited to one species of spider mite, Tetranychus urticae, Schausberger suspects it could be applicable to other species. “This guarding behavior is observed in several mite species, so I assume this undressing behavior will also be found in other spider mites, because they all have the same pressures – if they have to be the first mating partner then it’s very stressful for them when the female goes to comes out,” Schausberger said.

Tetranychus urticae Tetranychidae (red spider mite or two-spotted spider mite) is a species of herbivorous mite that infests many plants.

Dr. Yukie Sato, an assistant professor at the University of Tsukuba in Japan who was not involved in the paper, praised the study’s experimental design. “Many spider mite researchers have observed males helping females molt and wondered why the male’s mouth often touches the point where the female’s skin first breaks off when the male mounts,” Sato said. “This study is excellent evidence showing that males effectively help females molt and shorten the time to molt.”

While farmers and gardeners often vilify spider mites as herbivorous pests, many biologists use them as model organisms.

“Because they are so easy to raise in the lab, you can also ask them really cool basic behavioral questions. A lot of work has also been done on their genetics,” said Dr. Rebecca Schmidt-Jeffris, a research entomologist with the U.S. Department of Agriculture’s Agricultural Research Service, who was not involved in the study. “Very long down the road, maybe as people develop more very specific species pest control strategies, they might be able to exploit this behavior in some way. Like maybe you could make a spider mite that’s not good at guarding your partner.”

In the meantime, Schausberger said he hopes this study will lead people to rethink these oft-overlooked creatures. “I hope they’re fascinated by what kind of advanced behavior has evolved, even in tiny creatures like spider mites,” he said.

Kate Golembiewski is a Chicago-based freelance science writer who loves zoology, thermodynamics, and death. She hosts the comedy talk show ‘A Scientist Walks Into a Bar’.

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