Cannibal Moths Help Scientists Understand How Extreme Selfishness Evolves

Scientists have discovered a way to prevent cannibal moths from selfishly eating their brethren. All you need is the space to get to know yourself.

The Indian flour moth, or the pantry moth (Plodia interpunctella), is usually a voracious vegetarian, devouring flours, cereals, rice and other packaged foods like a young caterpillar. However, if there is not enough nutrition, or if there are too many moths in the brood, these larvae can sometimes battle each other, delighting in both strangers and relatives.

That’s brutal survival behavior, but new research suggests this moth-eat-moth mentality is not inherent to the species. In friendlier conditions, these insects can be quite friendly.

When the researchers directly manipulated the spacing of five moth populations, they found that the crowded conditions led to much less cannibalism in just ten generations.

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

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

The findings support a previously unproven 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, suggested that when the animals interact more, the rate of cannibalism decreases. That’s because the chance of meeting and eating your relatives is statistically more likely in a denser group, and in the end, that would be a disadvantage.

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

The new microevolutionary experiment tests this theory.

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

(Rudolf / Rice University)

Above: The sealed enclosures where the meal moths were raised included sticky foods (top) or foods that were easier to get through (bottom).

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

“Because they lay eggs in groups, they are more likely to stay in these small family groups on stickier foods that limit how quickly 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 was driving this change in cannibalism.”

In this scenario, it appears that the cost of cannibalism outweighs the benefits. Eating another moth could decrease competition and provide food, but in tight spaces a caterpillar is more likely to eat its sibling. Devouring relatives can undermine the continuation of their shared genes if it happens enough.

Over time, those moths with more cooperative impulses were the ones that survived in a stickier substance.

Whether this finding holds for other species remains to be seen, but the authors say their results hold “considerable potential” for nature to select 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 behaviors under certain conditions. Some signs of this have already been seen in yeast and bacteria when their spatial structure is changed. There is also some evidence that parasites are less virulent to their hosts when dispersal opportunities 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 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. strangers because they have to move often for work or other reasons, “explains Rudolf.

For decades evolutionary biologists have been fascinated by disinterested behavior and how it arises in the animal kingdom. However, extreme forms of selfish behavior have been relatively overlooked.

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

It is worth finding out more.

The study was published in Ecology lettering.

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