Study confirms evolutionary link between social structure and selfishness

Volker Rudolf is Professor of Biosciences at Rice University. Credit: Jeff Fitlow / Rice University

One of nature’s most prolific cannibals may be hiding in your pantry, and biologists have used it to show how social structure affects the evolution of selfish behavior.

The researchers revealed that the least selfish behavior evolved under living conditions that forced people to interact more frequently with their siblings. While the finding was verified with insect experiments, Rice University biologist Volker Rudolf said the evolutionary principle could be applied to study any species, including humans.

In a study published online this week in Ecology letteringRudolf, University of California Berkeley collaborator Mike Boots and their colleagues showed that they could drive the evolution of cannibalism in Indian meal moth caterpillars with simple changes to their habitats.

Also known as weevil moths and pantry moths, Indian flour moths are common pantry pests that lay eggs in cereals, flour, and other packaged foods. As larvae, they are vegetarian caterpillars with one exception: they sometimes eat each other, including their own brood mates.

In laboratory tests, the researchers showed that they could predictably increase or decrease rates of cannibalism in Indian meal moths by decreasing the distance between individuals and thus increasing the likelihood of “local” interactions between sibling larvae. In habitats where caterpillars were forced to interact more often with their siblings, less selfish behavior developed within 10 generations.

Rudolf, a professor of biosciences at Rice, said the rise in local interactions is running up against the evolution of selfish behaviors like cannibalism.

To understand why, suggest that imaginary behaviors can be ranked from least to most selfish.

“At one end of the continuum are altruistic behaviors, where an individual may be giving up their chance to survive or reproduce in order to increase the reproduction of others,” he said. “Cannibalism is at the other extreme. An individual increases his own survival and reproduction by literally consuming his own species.”

Rudolf said the study provided rare experimental proof of a key concept in evolutionary theory: As local interactions increase, so does the selective pressure against selfish behaviors. That’s the gist of a 2010 theoretical prediction by Rudolf and Boots, the corresponding author of the meal moth study, and Rudolf said the study’s findings confirmed the prediction.

“Families that were very cannibals just didn’t do as well in that system,” he said. “Families that were less cannibalistic had much less mortality and produced more offspring.”

In the meal moth experiments, Rudolf said it was fairly easy to ensure that the meal moth’s behavior was influenced by local interactions.

“They live off their food,” he said. “So we varied how sticky it was.”

Fifteen adult females were placed in various enclosures to lay eggs. The moths lay eggs in the food, and the larval caterpillars eat and live within the food until they pupate. Food was plentiful in all rooms, but varied in viscosity.

Does selfishness evolve?  Ask a cannibal

Indian meal moths were raised for successive generations in sealed enclosures where conditions were identical except for the stickiness of their food. In the enclosures (above) where the food was stickier, the caterpillars were more likely to interact with their siblings. Food moths with more local interactions with siblings developed less selfish behavior, as evidenced by lower rates of cannibalism, in 10 generations. Credit: Volker Rudolf / Rice University

“Because they lay eggs in groups, they are more likely to stay in these small family groups on stickier foods that limit how fast they can move,” Rudolf said. “It forced more local interactions, which, in our system, meant more interactions with siblings. That’s really what we think was driving this change in cannibalism.”

Rudolf said that the same evolutionary principle could also be applied to the study of human behavior.

“In societies or cultures that live in large family groups among close relatives, for example, you might expect to see less selfish behavior, on average, than in societies or cultures where people are more isolated from their families and more likely to be surrounded. from strangers because they have to move often for work or other reasons, “he said.

Rudolf has studied the ecological and evolutionary impacts of cannibalism for almost 20 years. He finds it fascinating, in part because it was misunderstood and little studied for decades. Generations of biologists had such a strong aversion to human cannibalism that they dismissed the behavior in all species as a “phenomenon of nature,” he said.

That finally began to slowly change a few decades ago, and cannibalism has now been documented in more than 1,000 species and is believed to occur in many more.

“It’s everywhere. Most animals that eat other animals are cannibals to some degree, and even those that don’t normally eat other animals, like the Indian meal moth, are often cannibals,” Rudolf said. “There is no moral attached to it. That is just a human perspective. In nature, cannibalism is simply getting other food.”

But cannibalism “has important ecological consequences,” Rudolf said. “It determines the dynamics of populations and communities, the coexistence of species and even entire ecosystems. It is definitely little studied due to its importance.”

He said the experimental follow-up to his theoretical work and Boots’s 2010 came almost by chance. Rudolf saw an epidemiological study that Boots published a few years later and realized that the same experimental setup could be used to test his prediction.

While the moth study showed that “limiting dispersal”, and therefore increasing local interactions, may counter the evolution of cannibalism by increasing the cost of extreme selfishness, Rudolf said the evolutionary drive can probably go as well. in the opposite direction. “If the feeding conditions are bad, cannibalism provides additional benefits, which could lead to more selfish behavior.”

He said it’s also possible that a third factor, kinship recognition, may also provide an evolutionary boost.

“If you’re really good at recognizing relatives, that limits the cost of cannibalism,” he said. “If you recognize relatives and avoid eating them, you can allow yourself to be much more cannibalistic in a mixed population, which can have evolutionary benefits.”

Rudolf said he plans to explore the three-way interplay between cannibalism, dispersal and kinship recognition in future studies.

“It would be nice to have a better understanding of the driving forces and to be able to further explain the variation that we see,” he said. “For example, why are some species extremely cannibalistic? And even within the same species, why are some populations much more cannibalistic than others? I don’t think that’s a single answer. But are there some basic principles that we can work? and test? Is it superspecific for each system or are there more general rules? “

Additional co-authors include Dylan Childs and Jessica Crossmore of the University of Sheffield, and Hannah Tidbury of the University of Sheffield and the Center for the Environment, Fisheries and Aquaculture Science in Weymouth, England.

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More information:
Mike Boots et al, Experimental Evidence that Local Interactions Select Against Selfish Behavior, Ecology lettering (2021). DOI: 10.1111 / ele.13734

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Citation: Study confirms the evolutionary link between social structure and selfishness (2021, March 25) retrieved March 25, 2021 from html

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