Cannibal butterflies help scientists understand how extreme selfishness evolves

Scientists have found a way to prevent cannibalistic butterflies from selfishly eating their siblings. All it takes is space to get to know each other.

Indian flour moth or pantry moth (Plodia interpunctella), is generally a voracious vegetarian, eating flours, grains, rice, and other packaged foods like a young caterpillar. However, if there is not enough food around, or if there are too many butterflies in the brood, these larvae can sometimes turn on each other, feasting on both strangers and parents.

It’s brutal survival behavior, but new research suggests this moth mentality is not inherent in the species. Under more friendly conditions, these insects can be quite neighbors.

When researchers directly manipulated the spacing of five populations of moths, they found that more demanding conditions led to far less cannibalism in just ten generations.

“Families that were very cannibalistic just didn’t do as well in this system,” says biologist Volker Rudolf of Rice University.

“Families that were less cannibalistic had much less mortality and produced more offspring.”

The results support a hitherto untested theory behind the evolution of social behavior. A team of researchers – including Rudolf and the first author of the moth study, Mike Boots, a biologist at the University of California at Berkeley – have suggested that when animals interact more, the rate of cannibalism decreases. This is because the chance to meet and eat your loved ones is statistically more likely in a denser group, and ultimately that would be at a disadvantage.

In short, the closer a family unit is, the less likely they are to kill each other.

The new microevolutionary experiment puts this theory to the test.

In the early stages of this particular butterfly’s life, caterpillars live and grow in their food, so the authors decided to limit the larvae’s ability to disperse by creating five different food viscosities of equal nutrition. Practically this meant that some conditions were easier for the caterpillars to move around, while other environments were more sticky and resulted in less movement and more interactions between individuals.

0324 CANNIBAL fig lg 620x620 1 (Rudolf / Rice University)

Above: The sealed enclosures where the flour moths were raised included either sticky foods (top) or foods that were easier to move (bottom).

After 10 generations, the researchers compared the rate of cannibalism in each group. In cases where dispersal was limited by stickiness, the extreme selfish behavior of cannibalism decreased significantly over time.

“Because they lay eggs in clusters, they are more likely to stay in these small family groups in stickier foods that limit the speed at which they can move,” says Rudolf.

“It forced more local interactions, which in our system meant more interactions with siblings. That’s really what we think is driving this change in cannibalism.”

In this scenario, it seems the cost of cannibalism outweighs the benefits. Eating another moth can decrease competition and provide food, but in tight spaces a caterpillar is more likely to eat its sibling. Devouring parents can interfere with the continuity of their shared genes if this happens enough.

Over time, those butterflies with more cooperative impulses are the ones that have survived in a more sticky substance.

Whether this finding holds true for other species remains to be seen, but the authors say their findings imply “considerable potential” for nature to choose against selfish behavior.

Natural selection is often described as an inherently selfish force, but this does not necessarily mean that there are no benefits to cooperative behavior under certain conditions. Some signs of this have already been seen in yeasts and bacteria when their spatial structure is altered. There is also some evidence that the parasites are less virulent to their hosts when the possibilities for dispersal are limited.

A similar situation could even occur between humans.

“In societies or cultures that live in large family groups among close relatives, for example, you may expect to see less selfish behavior, on average, than in societies or cultures where people are more isolated from their homes. family and more likely to be foreigners as they often have to move for work or other reasons, ”says Rudolf.

For decades, evolutionary biologists have been fascinated by altruistic behavior and the way it occurs in the animal kingdom. Extreme forms of selfish behavior, however, have been relatively overlooked.

Rudolf has spent decades trying to change that, and his new research on moths shows just how important cannibalism can be in the dynamic evolution of animals and their interactions and behaviors.

It is worth knowing more.

The study was published in Ecology letters.