Spider Personalities Can Hasten or Slow the Spread of Disease Through Colonies

July 11, 2016 | Erica Tennenhouse

Colonial spiders, Stegodyphus dumicola
Photo credit: Bernard DUPONT/Wikipedia (CC BY-SA 2.0)

Groups of only shy spiders get hit hard.

Like humans and many other animals, spiders possess personalities. Some display behaviors consistent with shyness, while others are deemed to be bold.

“’Boldness-shyness’ represents a behavioral spectrum on which animals can fall,” Carl Keiser, a biology graduate student at the University of Pittsburgh explains to The Science Explorer.

“It is a personality trait that we define as an individual animal’s propensity to engage in risky or dangerous activity like moving in the presence of a predator. Many animals fall somewhere along this spectrum, from fishes to butterflies and chimpanzees to spiders.”

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In a study published in the journal Biology Letters, a team of researchers led by Keiser and his advisor, Jonathan Pruitt, tested how diseases spread through groups composed of bold and shy social spiders in varying proportions.

The spiders were given personality tests, in which they were placed in a novel environment (in this case, a plastic container) and hit with two rapid puffs of air to simulate a predator’s approach. “This causes them to ‘death-feign’ and cease movement, and we simply measure the amount of time it takes for them to resume normal activity,” says Keiser. “Bold spiders resume activity quickly, shy spiders take longer.”

They were then split into 53 groups of 10 spiders, with a given group containing one of three personality compositions: all shy, 10 percent bold, or 40 percent bold. To each group, an 11th spider — an index case — that had been exposed to a naturally occurring bacteria was added to incite transmission of an infectious disease through the group.

24 hours later, the groups that contained 10 percent bold and 90 percent shy spiders had fared the best i.e., the bacteria spread through those groups to a lesser degree than it had in groups with either a greater number of bold individuals or only shy individuals.

Natural colonies of this species harbor only a small proportion of bold spiders, despite the fact that the groups forage more efficiently when they consist of many bold individuals. The researchers reason that having a small proportion of bold may provide benefits to colonies by keeping disease transmission to a minimum.

In terms of how human personality traits like sociability, shyness, and overall level of activity in one’s lifestyle influence one’s likelihood of encountering pathogens and sharing those microbes with their friends, Keiser says it’s easy to speculate but harder to make solid predictions. This is because experimental infection research, like this spider, cannot be conducted in humans.

“We have some post-hoc information about the traits that make some individuals more or less dangerous as the index case or ‘patient zero’ in an epidemic, but these studies always take place after the fact so it is hard to predict how future outbreaks might play out.”

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