Study confirms the evolutionary link between social structure and selfishness

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

The researchers revealed that less selfish behaviors evolved in living conditions that forced individuals to interact more often with siblings. Although the discovery was verified with experiments on insects, Rice University biologist Volker Rudolf said that the principle of evolution can be applied to study any species, including humans.

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

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

In laboratory tests, the researchers showed that they could predictably increase or decrease cannibalism rates in Indian moths, decreasing the distance that individuals could travel from one another and thus increasing the likelihood of “local” interactions between the siblings’ larvae. . In habitats where caterpillars were forced to interact more often with siblings, less selfish behavior has evolved in 10 generations.

Rudolf, a professor of biosciences at Rice, said the increase in local interactions piles the game against the evolution of selfish behaviors like cannibalism.

To understand why, he suggests that imaginary behaviors can be classified from the least to the 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 survival and reproduction by literally consuming his own species.”

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

“Families that were highly cannibalistic just did not do so well in this system,” he said. “Less cannibal families had far less mortality and produced more offspring.”

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

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

Fifteen adult females were placed in various pens to lay eggs. Moths lay eggs in food, and larval caterpillars eat and live within the food until they form a pupa. Food was plentiful in all areas, but varied in viscosity.

“Because they are laying eggs in groups, they are more likely to stay in these small family groups on the more sticky foods that limit how quickly they can move,” said Rudolf. “It forced more local interactions, which, in our system, meant more interactions with the brothers. This is really what we think was driving this shift in cannibalism.”

Rudolf said that the same evolutionary principle can 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 can 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 being surrounded by strangers because they often have to move to jobs or other reasons, “he said.

Rudolf has studied the ecological and evolutionary impacts of cannibalism for almost 20 years. He finds this fascinating, partly because it has been poorly understood and little studied for decades. Generations of biologists had such an aversion to human cannibalism that they described behavior in all species as an “aberration of nature,” he said.

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

“It’s everywhere. Most animals that eat other animals are cannibals to some extent, and even those that don’t normally eat other animals – like the Indian moth – are usually cannibals,” said Rudolf. “There is no morality attached to that. This is just a human perspective. In nature, cannibalism is just getting another meal.”

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

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

Although the moth study has shown that “limiting dispersion” and therefore increasing local interactions, can push against the evolution of cannibalism, increasing the cost of extreme selfishness, Rudolf said that the evolutionary impulse can probably go in the opposite direction as well . “If eating conditions are bad, cannibalism provides additional benefits, which can lead to more selfish behavior.”

He also said that it is possible that a third factor, kinship recognition, could also provide an evolutionary impetus.

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

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

“It would be nice to get a better understanding of the driving forces and be able to explain more about the variation that we see,” he said. “Like, 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 it’s going to be a single answer. But there are some basic principles that we can work with to test? Is it super specific for each system or are there more general rules? “

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