Does selfishness develop? Ask cannibals

HOUSTON – (March 25, 2021) – One of nature’s most prolific cannibals may be hiding in your pantry, and biologists have used it to show how social structure influences the development of selfish behavior.

Researchers revealed that less selfish behavior developed under living conditions that forced individuals to frequently interact with siblings. While the results have been verified through insect experiments, Rice University biologist Volker Rudolph said that the principle of evolution can be applied to studying any species, including humans.

In a study published online this week in Ecology LettersRudolph, longtime collaborator Mike Potts of the University of California, Berkeley, and colleagues showed that they could drive the evolution of cannibalism in the Indian meal moth larvae through simple changes in their habitats.

Also known as weevil mites and storehouse mites, they are common pantry pests that lay eggs in grains, flour, and other packaged foods. Caterpillars, they are vegetarian caterpillars with one exception: sometimes they eat each other, including their companions.

In laboratory tests, researchers have shown that they can increase or decrease cannibalism rates in Indian diet moths by reducing the distance individuals can roam from one another, thus increasing the likelihood of “local” interactions between sibling larvae. In habitats where the larvae are forced to interact often with siblings, less selfish behavior develops over 10 generations.

Rudolph, a professor of biosciences at Rice, said the increasing local interactions are stacking the deck against the evolution of selfish behaviors such as cannibalism.

To understand why, he suggests that visualizing behaviors can be categorized from least to most selfish.

“At one end of the continuum are altruistic behaviors, where an individual may give up his chance to survive or reproduce 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. ”

Rudolph said the study provided a rare experimental test of a key concept in evolutionary theory: As local interactions increase, the selective pressure against selfish behaviors increases. That’s the essence of the 2010 theoretical prediction by Rudolf and Boots, the corresponding author of the meal moth study, and Rudolf said the study results supported the prediction.

“Families that were highly cannibals did not do well in this system,” he said. “Families that were less cannibals had a much lower mortality rate and produced more offspring.”

In the meal moth experiments, Rudolph said it was fairly easy to confirm that the meal moth’s behavior was influenced by local reactions.

He said, “They live on their food.” “So we changed the range of viscosity.”

Fifteen adult females were placed in several containers to lay eggs. Moths lay eggs in food, and larvae eat larvae and live inside the food until they are pupated. Food was plentiful in all packages, but varied in viscosity.

“Because they lay eggs in groups, they are more likely to remain in these small family groups in foods that are more sticky and which limit their speed of movement,” said Rudolph. “It imposed more local interactions, which, in our system, meant more interactions with siblings. That’s really what we think was driving this change in cannibalism.”

Rudolph 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 between close relatives, for example, you might expect to see less selfish behavior, on average, compared to societies or cultures where people are more isolated from their families and more likely to be surrounded by strangers because they are They have to move a lot for jobs or other reasons.

Rudolph has studied the environmental and evolutionary impacts of cannibalism for nearly 20 years. He finds it fascinating, in part because he’s been misunderstood and misunderstood for decades. He said that generations of biologists have had such an aversion to cannibalism in humans that they write off the behavior in all species as “a nature freak.”

It finally started slowly changing a few decades ago, and cannibalism has now been documented in more than 1,000 species and is thought to occur in many others.

“It’s everywhere. Most of the animals that eat other animals are cannibals to some degree, and even those that don’t usually eat other animals – like the Indian meal moth – are often cannibals,” Rudolph said. . This is just a human perspective. In nature, cannibalism is just getting another meal. “

Rudolph said cannibalism “has important environmental consequences”. It defines the dynamics of people and societies, the symbiosis of species and even entire ecosystems. It has certainly been understood as important. “

He said the experimental follow-up of his 2010 theoretical paper was almost coincidental. Rudolph saw an epidemiological study published in Potts a few years later and realized that the same experimental setup could be used to test their predictions.

While the moth study showed that “reducing dispersion,” and thus increasing local interactions, could push against the evolution of cannibalism by increasing the cost of extreme selfishness, Rudolph said the evolutionary push might go the other way as well. “If the nutritional conditions are poor, then cannibalism provides additional benefits, which can drive more selfish behavior.”

He said it was also possible that a third factor, kin identification, could provide an evolutionary boost.

“If you are really good at getting to know relatives, it reduces the cost of cannibalism,” he said. “If you get to know relatives and avoid eating them, you can be a lot more cannibal in a mixed population, which can have evolutionary benefits.”

Rudolph said he plans to explore the triple interaction between cannibalism, dispersion, and kin identification in future studies.

“It would be good to have a better understanding of the driving forces and be able to explain more of the disparity that we see,” he said. “Like, why are some species so cannibals? And even within the same species, why do some populations eat more cannibals than others. I don’t think it will be a single answer. But are there some basic principles that we can work on and test? 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 Environment, Fisheries and Aquaculture in Weymouth, England.

The research was funded by the National Science Foundation (1256860, 0841686, 2011109), the National Institutes of Health (R01GM122061), and the Natural Environment Research Council (NEJ0097841).

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