The most aggressive spiders are not always the ones that bloom



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IMAGE: The African Social Spider Stegodyphus dumicola (S. dumicola)
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Credit: Noa Pinter-Wollman

Evolutionary biologists at McMaster University who study the social life and behavior of colony spiders – some of whom are docile and others aggressive – have found that the success of their cooperative societies depends on their neighbors.

The research, published in the journal Ecology and Evolution of Nature, sheds new light on the evolution of groups of animals that organize and hunt together.

"Consider the coordinated attacks of lion or wolf pride, or the dazzling behavior of starlings or shoals of sardines," says Jonathan Pruitt, an evolutionary biologist and president of Canada in the McMaster Department of Psychology, Neuroscience and Behavior.

"These societies are able to organize and execute strategies that can not be produced by isolated individuals. We wanted to see if the collective traits that enable success can depend on the traits of neighboring groups."

Researchers try to better understand successful collective hunting practices by studying the African social spider Stegodyphus dumicola (S. dumicola). While colonies of S. dumicola do not compete with each other face to face, a single plant can be home to several colonies, resulting in increased competition for flying prey.

Pruitt and his team traveled to two sites in Southern Africa and created "neighourhoods" or groups of competing spider colonies with very different foraging strategies: some colonies were dominated by docile hunting societies, while others were dominated by aggressive societies.

After comparing the aggressive and docile societies, the researchers found that any strategy that was in the minority was the best one.

When aggressive societies dominated the landscape, they overexploited resources, fueling an even greater need for prey to keep their social engines aggressive. Under these conditions, docile societies flourished because they could subsist on less and survived their aggressive rivals.

When docile societies dominated, researchers were surprised to find that there was no relationship between resource intake and reproductive success, suggesting that they operate well even with extremely low resources.

"The key here is that there is a trade-off between the ability to dominate and monopolize the resources of rivals and the ability to live a little," says Pruitt. "No single strategy completely annihilates the opposite strategy, and that is why we see various kinds of social characteristics maintained through evolutionary time."

Researchers are now working in Namibia to study neighborhood colonies that vary in size and density.

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Editors of attention: Photos of the S. dumicola spider can be downloaded at this link: https: //adobe.ly /2UOgufW

Please, credit: Noa Pinter-Wollman

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