Spider mite males ‘undress’ their partners to mate ASAP

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You can’t hurry love,” the Supremes sang, but in the animal kingdom, finding a potential mate as quickly as possible can be crucial for passing on genes.

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 mature 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, feeding on plants by piercing the tissues with their sharp mouthparts and sucking out the juices.

Living together in dense colonies can make for fierce competition in finding a mate, especially because female spider mites only use the sperm from the first male with which they mate. They even store this sperm in a specialized internal pouch to fertilize their eggs for the rest of their lives.

Since being the first to mate with a female is the only way for a male spider mite to pass along his genes, males have developed strategies to improve their chances. Males will guard females that are nearly mature, so that as soon as the females are set to mate, the males will be ready. Some males fight off competitors that approach the nearly adult females, while others, nicknamed “sneakers” by researchers, stealthily lie in wait. As soon as the female sheds her old skin and emerges as a mature adult, the males rush in.

Molt and mate

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

“We observed that the guarding male becomes highly active and starts to pull on the skin of the female and strip it off,” said Schausberger, who was the lead author of the new paper. “The males then pull off the hind parts (of the skin) to get access to the genital opening” to do the deed. “Sometimes they copulate when the front part (of the female) is still covered,” he said — there’s no time to fully undress.

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

Stiff competition

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 went faster and the males’ chances of being the first to mate were maximized. “Even a couple of minutes earlier, it pays for the guarding male to not lose his guarding investment to another one,” Schausberger said.

While this study was limited to one species of spider mite, Tetranychus urticae, Schausberger suspects that it could be applicable to other species. “This guarding behavior is observed in different mite species, so I assume that this undressing behavior will also be found in other spider mites, because they all have the same pressure — if they must be the first mating partner, then it’s highly stressful for them when the female comes out,” Schausberger said.

Dr. Yukie Sato, an assistant professor at the University of Tsukuba in Japan who was not involved with 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 is mounting,” Sato said. “This study is excellent evidence showing that males are effectively helping females molt and shortening the time to molt.”

Pests or tiny wonders?

While farmers and gardeners often revile spider mites as plant-eating pests, many biologists use them as model organisms.

“Because they’re so easy to rear in the lab, you can also ask these really cool basic behavioral questions of them. There’s also a lot of work that’s been done on their genetics,” said Dr. Rebecca Schmidt-Jeffris, a research entomologist at the US Department of Agriculture, Agricultural Research Service, who was not involved with the study. “Very long down the road, maybe as people are developing more very specific kinds of pest management strategies, maybe they could exploit this behavior in some way. Like maybe you could create a spider mite that’s not good at mate-guarding anymore.”

In the meantime, Schausberger said he hopes this study will lead people to reconsider these often overlooked creatures. “I hope they are fascinated about what type of sophisticated behaviors have evolved, even in such tiny animals as spider mites,” he said.

Kate Golembiewski is a freelance science writer based in Chicago who geeks out about zoology, thermodynamics and death. She hosts the comedy talk show “A Scientist Walks Into a Bar.”

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