These male spiders have adopted an unusual strategy to survive sexual cannibalism

A male spider weaves an orb and ejaculates a female after mating. Survival may mean another chance to fertilize her eggs.

Rudyard famous In a 1911 poem that “the female of the species is more dangerous than the male.” He specifically cited female bears and cobras, but the sentiment would certainly apply to many spider species, as some female spiders usually feed on males after mating – a behavior known as sexual cannibalism. males in one species of spider that weaves an orb (Philoponella prominensThey adopted an unusual defensive strategy, according to A . new paper Published in the journal Current Biology. They fling themselves away immediately after mating in hopes of getting another round before they are eaten – they often fly through the air too fast for a regular camera to pick up the details.

This species forms colonies in which the spiders have individual webs that are loosely linked to form a lumpy web complex, according to the authors. These community networks can harbor up to 215 spiders, with a male-to-female ratio of about 1.5. The team surveyed 477 community networks in the field, noting that female spiders rarely leave their networks and then usually only if the agglomerated web is destroyed. But male spiders moved from one web to another in search of mates once they reached full maturity.

And yes, females have proven to be particularly aggressive during the mating process, which often ends in sexual cannibalism. The male spiders that survived this fate were able to ejaculate quickly once mating was over. Male spiders usually produce a draft line that is attached to the female’s web during courtship, which remains in place during mating. Once the deed was completed and the female spider moved to attack, the male spider pushed itself away from the web and retreated to safety.

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For their lab experiments studying catapult behavior, the team collected spiders — both males and females just one iota away from adulthood — from the Wuhan East Lake Landscape Park in China. They were stored in flasks covered with foam and fed tasty fruit flies twice a week when they were ripe.

The scientists randomly selected an unmarried male and placed him in a breeding enclosure of a randomly selected unmarried female. The female spider had consumed about 20 fruit flies beforehand to ensure that she was not hungry. Then they recorded everything that happened during the next hour: courtship, palpation insertion, ejaculation, and whether the female spider attacked her mate and whether it survived. The team only used each spider once and then returned them to the wild (assuming they weren’t eaten).

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Zoom / two Philoponella prominens Spiders mate in a weave orb.

Xichang Chang

Of the 155 successful marriages, male spiders jumped after 152 of them, ensuring their survival. HD video recorded an average peak speed of 65 cm/sec, ranging from about 30 cm/sec to approximately 90 cm/sec. The average acceleration was about 100 m/s2Males descend at a rate of 175 times per second while in the air. The three men who did not ejaculate were killed in these experiments.

The authors conducted another set of experiments to determine whether male spiders’ ejaculatory behavior is an essential component of the mating process and to confirm that this behavior reduces the incidence of male eating by their mates. They placed a fine brush near the male’s back to prevent ejaculatory behaviour. All 30 of these spiders were killed, which clearly shows that if a male spider wants to avoid being eaten by his mate, he needs a catapult.

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How did the remaining spiders manage to jump so far? The team conducted experiments to determine if the safety streak was the cause of ejaculatory behavior, either by clipping the thread during mating or by applying a thin layer of superglue to the tips of male spiders’ spinnerets to prevent silk production. Males can still ejaculate.

Concluding that the legs were the primary mechanism, the team used a scanning electron microscope to look for any special physical structures that could lead to these ballistic jumping motions. They found that the supraspinal tibia joint had no extensor muscle, so male spiders could build hydraulic pressure by bending the joint against the female spider. When the joint is released, it expands rapidly and releases the male into the air. However, the researchers found no evidence of a locking mechanism to keep the legs focused during the push-up phase – an aspect that requires further research.

There are a number of hypotheses as to why sexual cannibalism occurs in nature. This study appears to support the ‘partner choice’ hypothesis. “We observed that males who could not perform ejaculation were disengaged by the female,” Co-author Shichang Zhang said from Hubei University in Wuhan, China. He indicates that this behavior evolved to combat cannibalism in females under the pressure of intense predation by females. Females may use this behavior to judge the quality of the male during mating. If the male cannot perform the ejaculation, he kills her, and if the male can perform it several times, she accepts her sperm.”

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Apparently, female spiders can mate up to five times with the same male, although it is not clear from this study how often a male spider would need to risk his life to successfully fertilize the female’s eggs. Chang and others. They believe their study is the first to show a strong link between surviving male cannibals and ‘locomotor performance’.

DOI: Current Biology, 2022. 10.1016 / j.cub.2022.03.051 (About DOIs).

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