Social susceptibility

January 02, 2018

This is the story of a spider, small but bold.

This particular arachnid, in fact, has helped to debunk the Great Man Theory, a 19th-century notion positing that highly influential individuals use their power -- be it personal charisma, intelligence, wisdom or political skill -- to maximize their impact in shaping the course of history. 

How better to test that theory than with Stegodyphus dumicola?

Working with these African social spiders in their native habitats, UC Santa Barbara evolutionary ecologist Jonathan Pruitt created a model for exploring leadership dynamics and social susceptibility -- the tendency of individuals to change their behavior in response to interactions with influential group members. He found that the social susceptibility of the population majority -- and not the influence of key individuals -- is what drives leadership. The results appear in the journal Current Biology.

"We knew from previous studies that in a social group, the rare presence of bold individuals -- who constitute between 1 and 5 percent of a population -- radically changes collective behavior," said Pruitt, an associate professor in UCSB's Department of Ecology, Evolution, and Marine Biology (EEMB). "This new research evaluates whether the rise and fall of societies could be contingent on having just one or a few of these key individuals and whether the profitability of their presence might change based on the environment."

Pruitt and his team set up 240 experimental societies across two different precipitation gradients in Africa: one in the Namib Desert heading north to Angola and a second from the Kalahari Desert heading east to Lesotho. Some of these colonies contained particularly bold spiders (putative leaders) and some did not. The researchers then monitored these colonies' behavior and survival for the next six months.

The scientists determined the boldness of individual spiders by exposing them to a directional jet of air. Because S. dumicola cannot see well, they interpret air movement as a predator such as a bird, bat or wasp. Their response? A death-feigning posture wherein they tuck their legs and huddle into a ball. Bold individuals don't hide for long, but shy ones can take 20 minutes to an hour to recover.

"We wanted to see whether the presence of these particularly bold individuals changed how a society behaves collectively, and whether the aggressiveness of a society determined the likelihood of its members surviving or dying together in a sudden extinction event," Pruitt explained. "We found no association between how a society behaved and whether it lived or died at wet sites; nor did bold individuals have a large effect on colony behavior at these sites. However, we found a very tight association between the presence of bold individuals and societal aggressiveness at arid sites, and colonies containing bold individuals were far more likely to survive in these habitats."

The fact that the same rare personality types existed at both dry and wet sites, but varied in their degree of apparent social influence across these habitats, allowed the investigators to decipher, for the first time, whether it is the traits of the leaders or the social context in which they reside that truly drives their influence. As it turned out, the population majority determined whether these key group members could emerge at all, thus debunking the Great Man Theory and its parallel hypotheses regarding "keystone individuals" in a variety of animal societies. Instead, social influence appears to emerge from shy, generic spiders.

"When we took bold individuals from a wet site, where they didn't have any social influence, and put them with shy spiders from an arid site, those shy individuals were willing to follow the bold ones regardless of where they were from," Pruitt noted. "So, it wasn't the unique social influence of bold individuals from arid sites but rather the social susceptibility of the population majority that made an advantageous social order emerge." 

To further scrutinize their findings, the scientists substituted bold individuals of another independently evolved species of social spider that occurs in southern Africa. Adding bold Stegodyphus mimosarum to groups of shy spiders in both wet and dry sites reproduced the same result at wet sites: The shy individuals were unresponsive to bold foreigners. However, the shy spiders from dry sites, who were used to food-restricted environments, responded equally to bold spiders of both species. Thus, for arid S. dumicola, anything even coarsely approximating the phenotype of a leader is enough to instigate followership in these populations.

"Shy S. dumicola from arid sites are susceptible to any indication of a bold individual in their groups, and the social susceptibility endemic to these sites succeeds in creating an advantage that increases a colony's chances of survival," Pruitt said.
-end-
UCSB EEMB co-authors are Colin Wright, James Lichtenstein and Ambika Kamath. Other contributors are Gregory Chism of the University of Arizona, Brendan McEwen of the University of Pittsburgh and Noa Pinter-Wollman of UCLA.

This research was supported by grants from the National Science Foundation's Division of Integrative Organismal Systems.

University of California - Santa Barbara

Related Behavior Articles from Brightsurf:

Variety in the migratory behavior of blackcaps
The birds have variable migration strategies.

Fishing for a theory of emergent behavior
Researchers at the University of Tsukuba quantified the collective action of small schools of fish using information theory.

How synaptic changes translate to behavior changes
Learning changes behavior by altering many connections between brain cells in a variety of ways all at the same time, according to a study of sea slugs recently published in JNeurosci.

I won't have what he's having: The brain and socially motivated behavior
Monkeys devalue rewards when they anticipate that another monkey will get them instead.

Unlocking animal behavior through motion
Using physics to study different types of animal motion, such as burrowing worms or flying flocks, can reveal how animals behave in different settings.

AI to help monitor behavior
Algorithms based on artificial intelligence do better at supporting educational and clinical decision-making, according to a new study.

Increasing opportunities for sustainable behavior
To mitigate climate change and safeguard ecosystems, we need to make drastic changes in our consumption and transport behaviors.

Predicting a protein's behavior from its appearance
Researchers at EPFL have developed a new way to predict a protein's interactions with other proteins and biomolecules, and its biochemical activity, merely by observing its surface.

Spirituality affects the behavior of mortgagers
According to Olga Miroshnichenko, a Sc.D in Economics, and a Professor at the Department of Economics and Finance, Tyumen State University, morals affect the thinking of mortgage payers and help them avoid past due payments.

Asking if behavior can be changed on climate crisis
One of the more complex problems facing social psychologists today is whether any intervention can move people to change their behavior about climate change and protecting the environment for the sake of future generations.

Read More: Behavior News and Behavior Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.