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When spiders leave the nest, they turn aggressive

By
Brooks Hays
The labyrinth spider acts aggressively toward other spiders, even its relatives, after dispersing to live a solitary existence. Photo by gailhampshire/Flickr
The labyrinth spider acts aggressively toward other spiders, even its relatives, after dispersing to live a solitary existence. Photo by gailhampshire/Flickr

July 2 (UPI) -- Spiders who exhibit sociability and tolerance when they're first born often become aggressive when they leave the nest and plot out on their own. Now, scientists are beginning to understand why.

Most spiders are solitary creatures and, like other solitary animals, solo spiders tend to behave aggressively toward other spiders. But most spiders aren't born aggressive. Spiderlings spend their earliest days living alongside their many brothers and sisters. During this developmental stage, young spiders exhibit mutual attraction and social tolerance.

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At some point, the young spiders disperse. Around the same time spiders set off on their own, the insects exhibit a sharp decline in social tolerance. It's a pattern of behavior observed among many species that exhibit sociality only transiently during their life cycle.

To better understand the relationship between dispersal and aggression, scientists in France studied the behavior of a solitary species, Agelena labyrinthica, the labyrinth spider, in a controlled setting.

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Scientists chose the labyrinth spider because it is common in France, and because it has pair relatives living in Equatorial Africa that are permanently social.

"The spider is highly relevant to launch comparative studies between solitary and social species with the aim of identifying the behavioral rules supporting their difference in sociality," Violette Chiara, a biologist at the University of Toulouse and the French National Center for Scientific Research, told UPI.

Researchers observed the spider's behavior as they developed and used their observations to build an interpretive model.

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"We modeled the behaviors of spiders using numerical simulations," Chiara said.

The model helped Chiara and her colleagues identify the behavior rules that govern dispersal.

"Agreement between the experimental and theoretical results in collective dynamics -- the initial clustering of spiderlings and then the dissociation of groups -- confirmed that we captured the main rules," Chiara said.

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Researchers were able to confirm that the development of mobility fully explains the timing of the spiderlings dispersal. Once the young spiders are physically capable of venturing out on their own, they light out for the territory.

Thus, scientists were able to conclude that dispersal is not caused by the loss of sociality and the onset of aggression. Instead, dispersal and life spent in solitude causes the development of aggression.

Researchers detailed their findings Tuesday in the journal PLOS Biology.

Though the study's authors aren't yet sure what precisely causes the development of a spider's aggressive disposition -- that's their next study -- they have some ideas.

"Our main hypothesis is that isolated spiderlings forget the social cues emitted by their siblings," Chiara said.

The latest findings and the biologists' followup research could offer new insights into the development of sociality and aggression among a wide array of species.

"There are many species of insects that are gregarious at the earliest developmental stages and that then develop a solitary life. Our findings may provide insights into the mechanisms leading to dispersal in such species, and where applicable, into the processes driving the onset of their aggressiveness," Chiara said.

"More broadly, we believe that identifying the mechanisms leading to dispersal in transiently gregarious species can be highly informative about the key mechanisms that have supported the many transitions to permanent sociality in diverse taxa."

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