Male Spiders Sacrifice Legs to Placate Cannibalistic Lovers
(Inside Science) -- Some male spiders sacrifice their own front legs to their female love interests to keep them distracted long enough to get busy.
A new study has found that a male tufted golden orb weaver spider will offer a female one of his front legs to snack on during sex, most likely to appease her and increase his chances of both successfully mating and escaping (relatively) uneaten.
“We have good evidence for this idea that it is a pacifying thing,” said Jutta Schneider, a behavioral ecology professor at the University of Hamburg in Germany and one of the co-authors of a recent study about the behavior published in Animal Behaviour. “[The offering] would give the male more time and peace to copulate.”
Tufted golden orb weavers (Trichonephila fenestrata) live in southern Africa. The males are much smaller than the females, and typically only mate with one female in their lifetime, partly because they don’t always survive the post-copulatory pillow talk and partly because their sexual strategy can preclude giving love a second chance. These males have two modified tubular organs called pedipalps that they place in one or both of the females’ two genital openings, sequentially. They then break them to deliver the sperm and act as a genital plug that blocks other males from subsequent mating attempts until the female has laid her eggs.
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Researchers have long known that spider males of many species are opportunistic maters. Often smaller than their aggressive and sometimes cannibalistic female counterparts, males sometimes jump in and mate with a female distracted by a meal.
But Schneider and her colleagues had observed that the male tufted golden orb weaver spiders took the initiative by offering females one of their front legs to feast on, actively casting it from their body (a process called autotomy) during copulation and continuing their business while she ate.
Schneider and her co-author designed experiments to test if this was actually a mating strategy. An earlier study had shown that females that were busy feeding wouldn’t eat attempted suitors.
The researchers conducted a new test to see first whether females had a particular thing for male legs. They found the females accepted male legs more often than similar-looking legs from insects. The researchers thought there might be some sort of coating or chemical attractant that draws the females to the males’ legs and even did a test offering legs washed with a solvent and those without, but it seemed to make no difference.
“It looks like a stick, there cannot be much in there to provide nourishment,” Schneider said, adding that they are still unclear why the females chose male legs.
To show that the males are giving up their legs strategically, the researchers did another experiment in which they gave the females legs from males at the right moment, when the male was trying to mate with them. They observed that the females who had been offered a leg were significantly less likely to attack the males.
“Spiders do a lot of weird and wonderful things in the name of sex,” said Catherine Scott, a postdoctoral biology researcher at Acadia University in Wolfville, Canada, who was not involved in Schneider’s study but who studies spiders. “I think it’s cool.”
Zachary Emberts, a postdoctoral fellow at the University of Arizona who wasn’t involved in this research but who studies autotomy in leaf-footed bugs, said that the process is usually associated with survival or escape, like when some lizard species drop their tails when chased by a predator.
He said that he knows of only one other example of a creature casting off legs as a reproductive strategy: Male nursery web spiders have been observed offering females their legs as a nuptial gift that allowed them to mate longer.
But the new study is important because it was backed up by lab experiments, he said. And unlike some species that will sacrifice body parts just to survive, it seems to show male tufted golden orb weavers do it for a combination of benefits -- the offering could increase their chances of mating and may also help them survive the encounter.
“It’s quite extreme for any organism to sacrifice part of its body,” Emberts said.
Scott points out that it could be worse. Male redback spiders sacrifice their entire body to females to mate, essentially giving their lives as a nuptial gift.
“[Sacrificing a leg] seems like a better idea because he survives,” Scott said of tufted golden orb weavers. “It speaks to the great variety of ways that male spiders do really interesting and sometimes kinky things in order to successfully mate with females.”
But there is still a cost. Even if the female doesn’t eat the rest of the male after copulation, he still usually sticks around to ward off other males attempting to mate with her.
“They are little fighting machines,” Schneider said. But already down one or two of legs, “this male has nothing to lose.”